Your FREE ACS General Chemistry Exam Practice Test 2026 – 240+ Q&A

Correct answer: $n = 2$ to $n = 1$

Correct answer: $n = 2$ to $n = 1$. Explanation: The emitted photon energy equals the difference between the levels, $\Delta E \propto \left(\frac{1}{n_f^{2}} - \frac{1}{n_i^{2}}\right)$. For $n = 2 \to 1$, $\Delta E \propto 1 - \frac{1}{4} = 0.75$; for $n = 5 \to 2$ it is $\frac{1}{4} - \frac{1}{25} = 0.21$; for $n = 3 \to 2$ it is $0.139$; for $n = 4 \to 3$ it is $0.049$. The largest energy gap, and thus the highest energy photon, is the $n = 2$ to $n = 1$ transition.

Correct answer: 2

Correct answer: 2. Explanation: According to the Pauli exclusion principle, an orbital can hold a maximum of two electrons, and these electrons must have opposite spins.

Correct answer: From 2s to 2p

Correct answer: From 2s to 2p. Explanation: The energy difference between the 2s and 2p orbitals in a multielectron atom is smaller compared to transitions involving a change in the principal quantum number. Therefore, it corresponds to the absorption of the lowest energy photon.

Correct answer: $[\ce{Ar}]$

Correct answer: $[\ce{Ar}]$. Explanation: The electron configuration of a neutral calcium atom is $[\ce{Ar}]4s^{2}$. When it forms a $\ce{Ca^2+}$ ion, it loses the two electrons in the 4s orbital, resulting in the configuration $[\ce{Ar}]$.

Correct answer: Isotopes of an element have different numbers of neutrons.

Correct answer: Isotopes of an element have different numbers of neutrons. Explanation: Isotopes of an element have the same number of protons (and hence are the same element) but differ in the number of neutrons.

Correct answer: Azimuthal quantum number ($l$)

Correct answer: Azimuthal quantum number ($l$). Explanation: The azimuthal quantum number ($l$) determines the shape of an electron orbital. For example, $l = 0$ corresponds to s orbitals (spherical), $l = 1$ to p orbitals (dumbbell-shaped), etc.

Correct answer: Electrons fill the orbitals of lowest energy first.

Correct answer: Electrons fill the orbitals of lowest energy first. Explanation: The Aufbau principle guides the building up of electron configurations for atoms in their ground states by filling the lowest energy orbitals before higher ones.

Correct answer: 9

Correct answer: 9. Explanation: The third energy level includes the 3s, 3p, and 3d sublevels, which have 1, 3, and 5 orbitals respectively. Thus, there are a total of 9 orbitals ($1+3+5$).

Correct answer: $1s^{2}2s^{2}2p^{5}3s^{1}$

Correct answer: $1s^{2}2s^{2}2p^{5}3s^{1}$. Explanation: This configuration shows an electron has been excited from the 2p orbital to the 3s orbital, which is typical of an excited state.

Correct answer: $4s^{2}3d^{10}4p^{5}$

Correct answer: $4s^{2}3d^{10}4p^{5}$. Explanation: Bromine (atomic number 35) has a ground state electron configuration of $[\ce{Ar}]4s^{2}3d^{10}4p^{5}$ for its outer shell, which accounts for the last 17 electrons.

Correct answer: Neon

Correct answer: Neon. Explanation: Neon, being the noble gas in Period 2, has a completely filled outer shell, making it very stable and requiring the most energy to remove an electron compared to other elements in its period.

Correct answer: Sodium

Correct answer: Sodium. Explanation: Sodium, being in Group 1, commonly loses one electron to form a +1 ion, aligning with its group characteristics in the periodic table.

Correct answer: -2

Correct answer: -2. Explanation: Elements in Group 16 typically exhibit a -2 oxidation state due to their tendency to gain two electrons to achieve a noble gas electron configuration.

Correct answer: Manganese

Correct answer: Manganese. Explanation: Manganese exhibits oxidation states up to +7, which is higher than the other listed transition metals, demonstrated by compounds like permanganate ($\ce{MnO4-}$).

Correct answer: Argon

Correct answer: Argon. Explanation: Atomic radius decreases across a period due to increasing nuclear charge attracting electrons more strongly. Argon, being the last element in the 3rd period, has the smallest atomic radius.

Correct answer: Group 18

Correct answer: Group 18. Explanation: Group 18 contains the noble gases, all of which are monatomic gases at room temperature due to their complete electron shells and lack of need to react to achieve stability.

Correct answer: Fluorine

Correct answer: Fluorine. Explanation: Fluorine is the most electronegative element on the periodic table, reflecting its strong tendency to attract electrons in chemical bonds.

Correct answer: 1

Correct answer: 1. Explanation: Group 1 elements (alkali metals) typically lose one electron to form cations with a +1 oxidation state due to their electronic configuration.

Correct answer: $s^2 p^1$

Correct answer: $s^2 p^1$. Explanation: Elements in Group 13 have three electrons in the outer shell, with the typical electron configuration being $s^2 p^1$, indicating two electrons in the s orbital and one in the p orbital.

Correct answer: Group 15 (the pnictogens)

This element is in Group 15. Group placement for main-group elements is set by the number of valence (highest-n) electrons: here the $4s^2 4p^3$ outer shell gives 5 valence electrons, placing it in Group 15. The filled $3d^{10}$ subshell is core-like and does not count toward the main-group number, so Group 5 is wrong; counting only p electrons (Group 13) or assuming a near-full p subshell (Group 17) also misreads the configuration.

Correct answer: One electron in each of the three 2p orbitals, all with parallel spins

The correct arrangement is one electron in each of the three 2p orbitals with parallel spins. Hund's rule of maximum multiplicity states that electrons singly occupy each orbital within a subshell before any orbital is doubly occupied, and these unpaired electrons adopt parallel spins to minimize electron-electron repulsion. The paired-orbital options violate Hund's rule by pairing electrons before all degenerate orbitals are half-filled.

Correct answer: A chlorine cation with a +1 charge

This species is a chlorine cation with a +1 charge. The element is determined solely by the proton number (atomic number), and 17 protons identifies chlorine, not sulfur (16) or argon (18). Charge equals protons minus electrons, so $17 - 16 = +1$, making it a cation; the -1 option reverses the relationship between protons and electrons.

Correct answer: $n = 2, l = 2, m_l = 0, m_s = +1/2$

The forbidden set is $n = 2, l = 2, m_l = 0, m_s = +1/2$. The angular momentum quantum number $l$ must range from 0 to $n-1$, so for $n = 2$ the only allowed $l$ values are 0 and 1; $l = 2$ is impossible at $n = 2$. The other three sets satisfy all rules: $l < n$, $m_l$ falls within $-l$ to $+l$, and $m_s$ is $\pm 1/2$.

Correct answer: It is the weighted average mass of chlorine's naturally occurring isotopes, weighted by their relative abundances

The atomic weight is the weighted average mass of chlorine's naturally occurring isotopes, weighted by their relative abundances. Because chlorine exists mainly as $\ce{^{35}Cl}$ and $\ce{^{37}Cl}$ in fixed proportions, the abundance-weighted mean lands near 35.45 rather than at an integer. Nuclear binding energy and electron mass produce only negligible effects, and a simple (unweighted) average of 35 and 37 would give 36, not 35.45.

Correct answer: Increasing effective nuclear charge more strongly attracts an added electron across the period

The primary reason is the increasing effective nuclear charge, which more strongly attracts an added electron across the period. As protons are added without adding a new shell, the net positive pull on incoming electrons grows, releasing more energy. Atomic radius actually decreases (not increases) across a period, no new shells are added within a period, and neutron count does not govern electron attraction.

Correct answer: $sp^{3}d^{2}$

Correct answer: $sp^{3}d^{2}$. Explanation: A central atom in a square planar molecular geometry typically exhibits $sp^{3}d^{2}$ hybridization, which accommodates the four bonds and two lone pairs arranged in a square planar structure.

Correct answer: $\ce{SO2}$

Correct answer: $\ce{SO2}$. Explanation: $\ce{SO2}$ (sulfur dioxide) has resonance structures due to the presence of a lone pair on the sulfur atom and double bonds that can delocalize electrons between the oxygen atoms.

Correct answer: s-p

Correct answer: s-p. Explanation: In methane ($\ce{CH4}$), the hydrogen's 1s orbital overlaps with the carbon's $sp^{3}$ hybrid orbital to form a sigma bond, which is an s-p overlap.

Correct answer: Sigma and delocalized pi bonding

Correct answer: Sigma and delocalized pi bonding. Explanation: Benzene has sigma bonds between adjacent carbon atoms and delocalized pi bonds above and below the plane of carbon atoms, contributing to its aromatic stability.

Correct answer: Nitrogen

Correct answer: Nitrogen. Explanation: Nitrogen ($\ce{N2}$) forms a diatomic molecule with a triple bond, representing the strongest bond among the options, which is characteristic due to its ability to share three pairs of electrons.

Correct answer: +1

The nitrogen carries a formal charge of +1. A neutral nitrogen atom has 5 valence electrons; in $\ce{NH4+}$ it has 0 lone-pair electrons and shares 8 bonding electrons across four N-H bonds, so $FC = 5 - 0 - (1/2)(8) = 5 - 4 = +1$. The +1 on nitrogen accounts for the overall +1 charge of the ammonium ion, since the four hydrogens each have a formal charge of 0.

Correct answer: Only the placement of electrons differs; the nuclei stay in the same positions, and the true structure is a hybrid of all contributors

Resonance structures differ only in where the electrons (lone pairs and pi bonds) are drawn; the positions of the atomic nuclei do not change. The actual molecule is a single resonance hybrid, a weighted average of the contributors, not a mixture that flips back and forth between separate real structures. This delocalization of electrons is why species like the nitrate ion have three equivalent bonds rather than one double and two single bonds.

Correct answer: A sigma bond forms by head-on (end-to-end) orbital overlap along the bond axis, while a pi bond forms by side-to-side overlap above and below the bond axis

A sigma bond results from head-on, end-to-end overlap of orbitals directly along the internuclear axis, giving electron density concentrated between the two nuclei. A pi bond results from side-to-side overlap of parallel p orbitals, placing electron density above and below the bond axis. The first bond between two atoms is always a sigma bond; additional bonds in a double or triple bond are pi bonds.

Correct answer: 1 sigma and 2 pi

A triple bond contains 1 sigma bond and 2 pi bonds. The first bond between the two nitrogen atoms is always a sigma bond from head-on overlap, and the two remaining bonds are pi bonds formed by side-to-side overlap of the two perpendicular sets of p orbitals. This gives $\ce{N2}$ a total bond order of 3, which is why it is exceptionally strong and unreactive.

Correct answer: Count total valence electrons, arrange the least electronegative atom (except H) as the central atom, form single bonds, then distribute remaining electrons as lone pairs to satisfy the octet rule, adding multiple bonds if needed

The correct procedure is to first total the valence electrons from all atoms (adjusting for ionic charge), place the least electronegative atom (other than hydrogen) in the center, connect atoms with single bonds, then distribute the remaining electrons as lone pairs to complete octets, converting lone pairs into double or triple bonds when the central atom is short of an octet. Hydrogen is never central and holds only 2 electrons, while the central atom is typically the least electronegative because it shares electrons with more neighbors.

Correct answer: Hydrogen atoms are usually placed on the outside (terminal positions) and hold a maximum of 2 electrons

Hydrogen is placed in a terminal (outer) position and can hold at most 2 electrons, since it has only a 1s orbital and achieves a duet rather than an octet. Hydrogen is never the central atom. The octet rule has well-known exceptions (such as boron with 6 electrons or sulfur and phosphorus expanding past 8), and the running total of valence electrons must always match the electrons placed in the final structure.

Correct answer: 2

$\ce{O2}$ has a bond order of 2, corresponding to a double bond. Applying bond order = (bonding - antibonding)/2 gives $(8 - 4)/2 = 2$. This double-bond character is consistent with experiment, and the molecular orbital picture also correctly predicts $\ce{O2}$'s two unpaired electrons, which make it paramagnetic.

Correct answer: 1.5

Each carbon-carbon bond in benzene has a bond order of 1.5. Because of resonance, the six pi electrons are delocalized evenly around the ring, so each C-C linkage is an average of one single bond and one double bond: $(1 + 2)/2 = 1.5$. This is why all six C-C bonds in benzene are equal in length, intermediate between a typical single and double bond.

Correct answer: $sp^{3}$

The carbon in methane is $sp^{3}$ hybridized. Mixing one 2s and three 2p orbitals produces four equivalent $sp^{3}$ hybrid orbitals that point toward the corners of a tetrahedron, giving the characteristic 109.5-degree bond angles. An $sp^{3}$ atom has a steric number of 4, meaning four regions of electron density (here, four bonding pairs) and no lone pairs.

Correct answer: $sp^{3}$

A steric number of 4 corresponds to $sp^{3}$ hybridization. The steric number is the count of sigma bonds plus lone pairs on the central atom, and four regions of electron density require four hybrid orbitals, formed by combining one s and three p orbitals. This is why water (two bonds plus two lone pairs) and ammonia (three bonds plus one lone pair) are both described as $sp^{3}$, even though their molecular shapes are bent and trigonal pyramidal.

Correct answer: $sp$

Each carbon in acetylene is $sp$ hybridized. A carbon involved in a triple bond has a steric number of 2 (one bond to hydrogen and one sigma bond to the other carbon), so it mixes one s and one p orbital to form two $sp$ hybrids, leaving two unhybridized p orbitals to make the two pi bonds. This $sp$ hybridization gives the molecule its linear shape with 180-degree bond angles, in contrast to the $sp^{2}$ carbons of ethene and the $sp^{3}$ carbon of methane.

Correct answer: As bond order increases from single to triple, bond energy increases and bond length decreases

As the carbon-carbon bond order rises from single to double to triple, the bond energy increases (348 to 614 to 839 kJ/mol) and the bond becomes shorter. Sharing more electron pairs pulls the nuclei closer and holds them more tightly, so higher bond order means a stronger, shorter bond that takes more energy to break. The triple bond is therefore the strongest and shortest, not the weakest, of the three.

Correct answer: Roughly 0.4 to 1.7, indicating unequal sharing of the bonding electrons

Correct answer: roughly 0.4 to 1.7, indicating unequal sharing of the bonding electrons. A bond with an electronegativity difference of about zero is nonpolar covalent, a difference of roughly 0.4 to 1.7 produces a polar covalent bond with partial charges, and a difference above about 1.7 to 2.0 is generally treated as predominantly ionic. These cutoffs are guidelines rather than rigid boundaries.

Correct answer: Bent (angular), with a bond angle of about 104.5 degrees

Correct answer: bent (angular), with a bond angle of about 104.5 degrees. The oxygen in water has four electron domains arranged tetrahedrally, but because two of those domains are lone pairs, the molecular shape considers only the atoms, giving a bent geometry. Lone-pair repulsion compresses the H-O-H angle below the ideal 109.5 degrees to roughly 104.5 degrees.

Correct answer: Both shared electrons originate from a single atom rather than one electron from each atom

Correct answer: both shared electrons originate from a single atom rather than one electron from each atom. In a coordinate covalent bond, one atom donates a lone pair that is shared with an atom or ion that has an empty orbital, such as the bond formed when ammonia donates its lone pair to a hydrogen ion to make the ammonium ion ($\ce{NH3 + H+ -> NH4+}$). Once formed, a coordinate covalent bond is otherwise identical to any other covalent bond.

Correct answer: The molecule is linear and symmetric, so the two equal bond dipoles point in opposite directions and cancel

Correct answer: the molecule is linear and symmetric, so the two equal bond dipoles point in opposite directions and cancel. Although each carbon-oxygen bond is polar, the linear $\ce{O=C=O}$ arrangement places the two bond dipoles 180 degrees apart with equal magnitude, so their vector sum is zero. Geometry can therefore make a molecule with polar bonds nonpolar overall.

Correct answer: Boron is surrounded by only six bonding electrons (three bonds), an incomplete octet

Correct answer: boron is surrounded by only six bonding electrons (three bonds), an incomplete octet. Boron has three valence electrons and commonly forms three single bonds, leaving it electron-deficient with only six electrons around it rather than eight. This electron deficiency makes $\ce{BF3}$ a strong Lewis acid that readily accepts an electron pair.

Correct answer: Higher ionic charges and smaller distances between ion centers

Correct answer: higher ionic charges and smaller distances between ion centers. Lattice energy magnitude is proportional to the product of the ionic charges and inversely proportional to the distance between ion centers, so compounds with highly charged, small ions have the largest lattice energies. For example, $\ce{MgO}$ has a much greater lattice energy than $\ce{NaCl}$ because its ions carry $\ce{2+}$/$\ce{2-}$ charges and are relatively small.

Correct answer: Bond length decreases as bond order increases

Correct answer: bond length decreases as bond order increases. Higher bond order means more shared electron pairs pulling the nuclei closer together, so a triple bond is shorter than a double bond, which is shorter than a single bond between the same two atoms. This shortening also corresponds to a stronger, higher-energy bond.

Correct answer: It is a period 3 or higher element with accessible d orbitals (or low-lying orbitals) allowing more than eight electrons

Correct answer: it is a period 3 or higher element with accessible d orbitals (or low-lying orbitals) allowing more than eight electrons. Elements in the third period and below can accommodate an expanded octet, so phosphorus surrounds itself with ten electrons (five P-Cl bonds) in $\ce{PCl5}$. Second-period elements such as nitrogen cannot expand their octet because they lack available d orbitals.

Correct answer: Seesaw

Correct answer: Seesaw. Explanation: A molecule with a steric number of 5 has a trigonal bipyramidal electron-pair geometry. With one lone pair (placed in an equatorial position to minimize repulsion), the four bonding pairs adopt a seesaw molecular geometry.

Correct answer: 90 degrees

Correct answer: 90 degrees. Explanation: In a T-shaped molecular geometry, which arises from a trigonal bipyramidal electron pair geometry with two lone pairs, the bond angles between the bonded atoms are approximately 90 degrees.

Correct answer: Carbon dioxide ($\ce{CO2}$)

Correct answer: Carbon dioxide ($\ce{CO2}$). Explanation: Carbon dioxide is nonpolar because it has a linear geometry where the dipole moments of the polar $\ce{C=O}$ bonds cancel out, resulting in no overall dipole moment.

Correct answer: Electron-withdrawing by resonance

Correct answer: Electron-withdrawing by resonance. Explanation: The nitro group is an electron-withdrawing group both by resonance and induction due to its strong electronegativity and the ability to stabilize negative charge via resonance when attached to a conjugated system like benzene.

Correct answer: Tetrahedral

Tetrahedral is correct. When a central atom has four electron domains that are all bonding pairs and no lone pairs, valence shell electron pair repulsion (VSEPR) theory predicts the four pairs spread as far apart as possible, giving a tetrahedral shape with ideal bond angles of 109.5 degrees, as in methane ($\ce{CH4}$). Square planar and octahedral require six electron domains, so they do not apply to a four-domain center.

Correct answer: Trigonal planar, 120 degrees

Trigonal planar with 120-degree bond angles is correct. On a VSEPR chart, three electron domains with no lone pairs arrange themselves in a flat triangle around the central atom, giving 120-degree angles, as seen in $\ce{BF3}$ and $\ce{BCl3}$. Trigonal pyramidal and bent both require at least one lone pair, and linear corresponds to only two domains.

Correct answer: Linear

Linear is correct. A molecular geometry chart shows that two electron domains with no lone pairs point in exactly opposite directions, producing a linear shape with a 180-degree bond angle. In $\ce{CO2}$ the two C=O double bonds each count as a single domain, so the molecule is linear. A bent shape only results when lone pairs are present on a two-bond center, as in water.

Correct answer: 104.5 degrees, because two lone pairs on oxygen compress the bonding angle

104.5 degrees, caused by lone-pair repulsion, is correct. Oxygen in water has four electron domains (two bonding pairs and two lone pairs), so the underlying electron geometry is tetrahedral, but the two lone pairs push harder on the bonding pairs than the bonding pairs push on each other. This compresses the H-O-H angle from the ideal 109.5 degrees down to about 104.5 degrees. The 107-degree value applies to ammonia, which has only one lone pair.

Correct answer: The number of bonding domains and the number of lone pairs

The number of bonding domains and the number of lone pairs is correct. To determine molecular geometry, you draw the Lewis structure, then count the electron domains around the central atom, separating them into bonding pairs and lone pairs. The total gives the electron geometry, and subtracting the lone pairs gives the molecular shape. Atomic mass, proton count, and physical properties such as boiling point do not set the geometry.

Correct answer: Trigonal pyramidal

Trigonal pyramidal is correct. With four electron domains the electron geometry is tetrahedral, but replacing one bonding pair with a lone pair removes one visible vertex, leaving a three-legged pyramid shape, as in ammonia ($\ce{NH3}$) with bond angles near 107 degrees. A pure tetrahedral shape requires four bonding pairs and no lone pair, and bent requires two lone pairs.

Correct answer: Electron-domain geometry counts all bonding pairs and lone pairs, while molecular geometry describes only the arrangement of bonded atoms

Counting all domains versus only bonded atoms is the correct distinction. Electron-domain (or electron-pair) geometry is set by the total number of bonding and lone-pair domains, while molecular geometry describes the shape outlined by the nuclei of the bonded atoms only. For example, water has a tetrahedral electron geometry but a bent molecular geometry because its two lone pairs are not counted as atoms.

Correct answer: From the less electronegative atom toward the more electronegative atom

From the less electronegative atom toward the more electronegative atom is correct. The more electronegative atom pulls bonding electrons closer, gaining a partial negative charge, while the other atom is left partially positive. By convention the dipole moment arrow points from the partial-positive end toward the partial-negative (more electronegative) end. It has nothing to do with atomic mass and lies along the bond, not perpendicular to it.

Correct answer: Debye

The debye is correct. A dipole moment equals the magnitude of the separated charge times the distance between the charges, and chemists report it in debye units (1 D is about $3.34 \times 10^{-30}$ coulomb-meters). A larger debye value means greater charge separation and a more polar molecule. The joule measures energy, the pascal measures pressure, and the mole counts particles, so none of these describe a dipole moment.

Correct answer: A symmetric arrangement of bonds that causes the individual bond dipoles to cancel

Symmetric bond arrangement causing cancellation is correct. When polar bonds point in directions that balance one another, such as the three B-F bonds of trigonal planar $\ce{BF3}$ set 120 degrees apart or the two opposed C=O bonds in linear $\ce{CO2}$, their dipole vectors sum to zero. The molecule is therefore nonpolar overall even though each bond is polar. If there were no electronegativity difference, the bonds would not be polar in the first place.

Correct answer: Check whether the bonds are polar, then check whether the molecular shape leaves the bond dipoles uncanceled

Checking bond polarity and then molecular symmetry is the correct two-step test. A molecule is polar only if it contains polar bonds and its geometry does not arrange those bond dipoles symmetrically enough to cancel. Water is polar because its bent shape leaves a net dipole, while $\ce{CO2}$ is nonpolar because its linear shape cancels the two bond dipoles. Molar mass, atom count, and metal versus nonmetal classification do not determine molecular polarity directly.

Correct answer: Carbon tetrachloride ($\ce{CCl4}$)

Carbon tetrachloride ($\ce{CCl4}$) is correct. Although each C-Cl bond is polar, the four bonds point toward the corners of a symmetric tetrahedron, so their dipole vectors sum to zero and the molecule is nonpolar. $\ce{HCl}$ has a single polar bond and is clearly polar, $\ce{CH3Cl}$ lacks the symmetry to cancel its dipoles, and $\ce{SO2}$ is bent with a lone pair on sulfur, giving it a net dipole.

Correct answer: The bent shape prevents the bond dipoles from canceling, so the molecule is polar

The bent shape makes the molecule polar is correct. In a linear $\ce{AB2}$ molecule the two bond dipoles point in opposite directions and cancel, but bending the molecule (as lone pairs do in water or $\ce{SO2}$) means the two bond dipoles no longer oppose each other directly, leaving a net dipole moment. This is why water is polar while linear $\ce{CO2}$ is not. Lone pairs strongly influence both shape and polarity, and the bonding remains covalent.

Correct answer: Octahedral

The molecular geometry of $\ce{SF6}$ is octahedral. With six bonding domains and zero lone pairs (steric number 6), the six fluorine atoms arrange themselves symmetrically around sulfur with 90-degree bond angles, which is the defining octahedral shape. Square planar and square pyramidal arise only when one or two of those six domains are lone pairs, and trigonal bipyramidal corresponds to a steric number of 5.

Correct answer: T-shaped

The resulting molecular geometry is T-shaped. A steric number of 5 gives a trigonal bipyramidal electron-domain geometry; placing two lone pairs in the larger equatorial positions to minimize repulsion leaves the three bonded atoms arranged in a T shape. A seesaw shape arises from only one lone pair, while trigonal planar and linear correspond to lower steric numbers.

Correct answer: A larger electronegativity difference increases the bond's polarity by producing a greater separation of partial charge

A larger electronegativity difference increases the bond's polarity by producing a greater separation of partial charge. The more electronegative atom pulls the shared electron pair toward itself, creating larger partial negative and partial positive charges on the two atoms. A small difference yields a nearly nonpolar bond, so the relationship is direct, not absent or inverted.

Correct answer: Trigonal pyramidal with bond angles of about 107 degrees

Ammonia is trigonal pyramidal with bond angles of about 107 degrees. The four electron domains give a tetrahedral electron-domain geometry, but because one domain is a lone pair, the three N-H bonds form a pyramid. The lone pair repels the bonding pairs slightly more than they repel one another, compressing the ideal 109.5-degree tetrahedral angle to roughly 107 degrees.

Correct answer: It donates electron density into the ring through resonance, activating it toward electrophilic substitution

The methoxy group donates electron density into the ring through resonance, activating it toward electrophilic substitution. A lone pair on the oxygen overlaps with the ring's pi system, increasing electron density (especially at the ortho and para positions). This makes $\ce{-OCH3}$ an activating, ortho/para-directing substituent, in contrast to electron-withdrawing groups like nitro that deactivate the ring.

Correct answer: The linear, symmetric arrangement points the two bond dipoles in opposite directions so they cancel to a net dipole of zero

$\ce{CO2}$ is nonpolar because its linear, symmetric arrangement points the two bond dipoles in opposite directions so they cancel to a net dipole of zero. The central carbon has two bonding domains and no lone pairs, giving a 180-degree O=C=O geometry. Each C=O dipole is equal in magnitude but opposite in direction, so their vector sum is zero despite the individual bonds being polar.

Correct answer: Structure determines function: a molecule's shape governs how it interacts with other molecules

The relationship is best described by the principle that structure determines function: a molecule's shape governs how it interacts with other molecules. Differences in geometry change polarity, the ability to fit into binding sites, and intermolecular contacts, which in turn change reactivity and physical behavior. The molecular formula alone is insufficient because identical formulas can adopt different shapes with distinct properties.

Correct answer: Trigonal bipyramidal, with 120-degree angles in the equatorial plane and 90-degree angles to the axial positions

VSEPR predicts a trigonal bipyramidal geometry, with 120-degree angles in the equatorial plane and 90-degree angles to the axial positions. Five bonding domains and no lone pairs (steric number 5) split the positions into three equatorial atoms separated by 120 degrees and two axial atoms perpendicular to that plane. Square pyramidal and octahedral require a steric number of 6, and tetrahedral requires a steric number of 4.

Correct answer: Hydrogen bonding

Correct answer: Hydrogen bonding. Explanation: Hydrogen bonding, a strong type of dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms (like oxygen in water), is responsible for the high boiling point of water compared to molecules like hydrogen sulfide, which mainly exhibit weaker dipole-dipole interactions.

Correct answer: Low compressibility

Correct answer: Low compressibility. Explanation: Gases are highly compressible due to the large amount of space between particles, unlike liquids and solids which are relatively incompressible.

Correct answer: Decreasing the temperature

Correct answer: Decreasing the temperature. Explanation: Gas solubility increases as temperature decreases, because the dissolved gas molecules lose kinetic energy and are less likely to escape the solution. (Higher pressure of the gas above the liquid also increases solubility, per Henry's Law.)

Correct answer: Color of the solute

Correct answer: Color of the solute. Explanation: The color of the solute does not influence the rate of dissolution, whereas temperature, surface area, and agitation all do.

Correct answer: Ideal solutions

Correct answer: Ideal solutions. Explanation: Raoult's Law states that the partial vapor pressure of each component in an ideal solution is directly proportional to its mole fraction. It applies to ideal solutions, where interactions between different molecules are similar to those between similar molecules.

Correct answer: It increases the boiling point.

Correct answer: It increases the boiling point. Explanation: Adding a non-volatile solute to a solvent increases the boiling point of the solution, a phenomenon known as boiling point elevation, which is due to the lowering of the vapor pressure.

Correct answer: Molecules in gases move faster and are further apart than in liquids.

Correct answer: Molecules in gases move faster and are further apart than in liquids. Explanation: In gases, molecules move faster and are spaced further apart compared to liquids, leading to higher kinetic energy and lower intermolecular forces.

Correct answer: It is lower than the vapor pressure of the pure solvent.

Correct answer: It is lower than the vapor pressure of the pure solvent. Explanation: The presence of a non-volatile solute reduces the vapor pressure of a solution relative to the pure solvent due to the reduction in the mole fraction of the solvent, known as vapor pressure lowering.

Correct answer: The temperature and pressure above which a liquid can no longer exist.

Correct answer: The temperature and pressure above which a liquid can no longer exist. Explanation: The critical point marks the temperature and pressure above which distinct liquid and gas phases no longer exist; beyond it the substance becomes a single supercritical fluid.

Correct answer: Ion-dipole > hydrogen bonding > dipole-dipole > London dispersion

Ion-dipole > hydrogen bonding > dipole-dipole > London dispersion is the correct order of strength when molecules are similar in size. Ion-dipole forces (between an ion and a polar molecule, as when $\ce{NaCl}$ dissolves in water) are strongest; hydrogen bonding is the strongest force among neutral pure liquids; ordinary dipole-dipole forces are weaker; and London dispersion forces, present in all substances, are the weakest. This size caveat matters because in very large molecules dispersion forces can overtake the others.

Correct answer: Nitrogen, oxygen, or fluorine

Nitrogen, oxygen, or fluorine are the only atoms that, when directly bonded to hydrogen, produce a true hydrogen bond. These three are small and highly electronegative, so the H-N, H-O, and H-F bonds are strongly polarized, leaving the hydrogen partially positive enough to attract a lone pair on an N, O, or F of a neighboring molecule. Hydrogen attached to carbon or chlorine does not meet the electronegativity-plus-small-size requirement, so molecules like $\ce{CH4}$ and $\ce{HCl}$ do not hydrogen bond.

Correct answer: $\ce{I2}$ has far more electrons, giving it much larger London dispersion forces

$\ce{I2}$ has far more electrons and a larger, more polarizable electron cloud, producing much stronger London dispersion forces than $\ce{F2}$. Both halogens are nonpolar diatomics whose only intermolecular force is dispersion, but dispersion strength grows with the number of electrons and molecular size, so the heavier $\ce{I2}$ has a high enough boiling point to be a solid while the light $\ce{F2}$ stays a gas. Neither halogen can hydrogen bond, and both are nonpolar, ruling out the other explanations.

Correct answer: Dipole-dipole attractions arising from its polar C=O bond

Dipole-dipole attractions from acetone's polar carbonyl (C=O) bond raise its boiling point relative to nonpolar molecules of similar mass. Because the carbon-oxygen double bond is strongly polar, each acetone molecule has a permanent dipole, and these partial-positive and partial-negative ends attract neighboring molecules. Acetone cannot hydrogen bond with itself because its hydrogens are attached only to carbon, not to N, O, or F.

Correct answer: Lower vapor pressure and higher viscosity

Lower vapor pressure and higher viscosity both signal stronger intermolecular forces. Strong attractions hold molecules in the liquid, so fewer escape into the vapor phase (low vapor pressure) and the molecules resist flowing past one another (high viscosity). Weaker forces give the opposite: more molecules escape easily (high vapor pressure) and the liquid flows readily (low viscosity), so pairing high vapor pressure with high viscosity is internally inconsistent.

Correct answer: Its extensive hydrogen bonding pulls surface molecules strongly inward and together

Extensive hydrogen bonding is the answer. Surface tension reflects the inward cohesive pull on molecules at a liquid's surface; water's network of strong O-H...O hydrogen bonds creates a large net inward force, giving it a much higher surface tension than liquids that rely only on weaker dispersion or dipole-dipole forces. Dispersion forces in water are minor, water is polar, and low molar mass alone does not raise surface tension.

Correct answer: Adhesion between water and glass together with cohesion among water molecules

Adhesion to glass combined with cohesion among water molecules is correct. Capillary rise occurs because water adheres to the polar glass surface (adhesive forces) while hydrogen bonding holds the water column together (cohesive forces); the narrower the tube, the higher the rise. Cohesion alone, gravity, or ionic bonding does not account for the rise.

Correct answer: Xenon's larger, more polarizable electron cloud produces the strongest London dispersion forces

Xenon's larger, more polarizable electron cloud giving the strongest London dispersion forces is correct. All noble gases are nonpolar single atoms, so dispersion is their only intermolecular force; the heavier the atom, the more electrons and the greater the polarizability, producing stronger temporary dipoles and a higher boiling point. Noble gases form no hydrogen bonds or permanent dipoles.

Correct answer: The linear shape of n-pentane allows greater surface contact and stronger dispersion forces

The greater surface contact of linear n-pentane producing stronger dispersion forces is correct. For isomers of equal mass, molecular shape governs London dispersion strength: the extended linear chain of n-pentane offers more surface area for contact between molecules than the compact, nearly spherical neopentane, so its dispersion forces and boiling point are higher. The molecules are nonpolar, neither hydrogen bonds, and their masses are equal.

Correct answer: "Like dissolves like": nonpolar $\ce{I2}$ mixes with nonpolar $\ce{CCl4}$ through compatible dispersion forces

"Like dissolves like," with nonpolar $\ce{I2}$ mixing with nonpolar $\ce{CCl4}$, is correct. A solute dissolves best in a solvent with similar polarity and intermolecular forces; nonpolar iodine interacts well through dispersion forces with nonpolar $\ce{CCl4}$, but cannot disrupt water's strong hydrogen-bonding network. Iodine does not hydrogen bond, water's forces are stronger, and $\ce{CCl4}$ is less polar than water.

Correct answer: Ion-dipole attractions form between the ions and the polar water molecules

Ion-dipole attractions between the ions and polar water molecules is correct. When an ionic compound dissolves, the partial charges on polar water molecules orient toward the ions, surrounding each ion in a hydration shell; these ion-dipole interactions are relatively strong and release energy (hydration energy). Hydrogen bonding, dispersion, and new covalent bonds do not describe ion solvation.

Correct answer: Ethanol's O-H group lets it form hydrogen bonds, which the ether cannot

Ethanol's O-H group allowing hydrogen bonding is correct. Although both isomers have the same formula and mass, only ethanol has a hydrogen atom bonded directly to oxygen, enabling strong hydrogen bonds between molecules; dimethyl ether has no O-H bond and relies on weaker dipole-dipole forces, so it boils much lower. Neither is ionic, dispersion is comparable, and the masses are equal.

Correct answer: Solubility increases in direct proportion to the partial pressure

Solubility increasing in direct proportion to partial pressure is correct. Henry's law states that the concentration of a dissolved gas is directly proportional to the partial pressure of that gas above the solution, which is why carbonated beverages hold more $\ce{CO2}$ under pressure. Solubility does not decrease, remain constant, or require a threshold.

Correct answer: Disrupts orderly crystal formation, requiring a lower temperature for the solvent to freeze

Disrupting orderly crystal formation so a lower temperature is needed to freeze is correct. A nonvolatile solute interferes with the solvent molecules' ability to arrange into a solid lattice, so the freezing point is depressed; freezing-point depression depends on the number of dissolved particles, not their identity. The solute lowers (not raises) the freezing point, no reaction is required, and the effect is real and concentration-dependent.

Correct answer: They are weak nonpolar dispersion forces, allowing sublimation at ordinary pressure

Weak nonpolar dispersion forces allowing sublimation is correct. $\ce{CO2}$ is a linear nonpolar molecule held together only by relatively weak London dispersion forces, and its phase diagram places the liquid region above atmospheric pressure, so at ordinary pressure the solid sublimes directly to gas. $\ce{CO2}$ forms no hydrogen bonds, is not ionic, and has no net dipole.

Correct answer: Extensive hydrogen bonding among its sugar molecules resists flow

Extensive hydrogen bonding among its sugar molecules is correct. Viscosity measures a liquid's resistance to flow and increases with stronger intermolecular attractions; the many hydroxyl groups on dissolved sugars in honey form abundant hydrogen bonds that strongly resist molecules sliding past one another. Honey is polar, its forces are stronger than water's, and viscosity does depend on intermolecular forces as well as temperature.

Correct answer: 216 grams

Correct answer: 216 grams. Explanation: The reaction is $\ce{2Na + Cl2 -> 2NaCl}$. Sodium has a molar mass of about 23 g/mol, so 85 grams of $\ce{Na}$ is about $\frac{85}{23} = 3.70$ moles, which produces 3.70 moles of $\ce{NaCl}$. Since the molar mass of $\ce{NaCl}$ is about 58.5 g/mol, $3.70 \times 58.5 \approx 216$ grams.

Correct answer: 120 grams

Correct answer: 120 grams. Explanation: The molar mass of $\ce{CuSO4}$ (copper (II) sulfate) is approximately 160 g/mol. For 0.75 moles, the mass required is $0.75 \times 160 = 120$ grams.

Correct answer: 15 moles

Correct answer: 15 moles. Explanation: The balanced equation for the combustion of propane is $\ce{C3H8 + 5O2 -> 3CO2 + 4H2O}$. For every mole of propane burned, 3 moles of $\ce{CO2}$ are produced. Thus, $5 \times 3 = 15$ moles of $\ce{CO2}$ are produced.

Correct answer: $\ce{Al}$

Correct answer: $\ce{Al}$. Explanation: The balanced equation is $\ce{4Al + 3O2 -> 2Al2O3}$. Aluminum has a molar mass of about 27 g/mol, so 3.0 g of $\ce{Al}$ is about 0.111 moles. Oxygen has a molar mass of about 32 g/mol, so 4.0 g of $\ce{O2}$ is about 0.125 moles. Reacting 0.111 mol $\ce{Al}$ requires $0.111 \times \frac{3}{4} = 0.083$ mol $\ce{O2}$; since 0.125 mol $\ce{O2}$ is available, $\ce{O2}$ is in excess and $\ce{Al}$ is the limiting reagent.

Correct answer: 12.0 grams

Correct answer: 12.0 grams. Explanation: The balanced equation is $\ce{4Fe + 3O2 -> 2Fe2O3}$. Iron has a molar mass of 55.85 g/mol, so 8.4 grams of iron is about 0.150 moles. The 4:2 mole ratio of $\ce{Fe}$ to $\ce{Fe2O3}$ gives $0.150 \times \frac{2}{4} = 0.075$ moles of $\ce{Fe2O3}$. The molar mass of $\ce{Fe2O3}$ is about 159.7 g/mol, giving $0.075 \times 159.7 \approx 12.0$ grams.

Correct answer: 154.2 L

Correct answer: 154.2 L. Explanation: The balanced equation for the combustion of butane is $\ce{2C4H10 + 13O2 -> 8CO2 + 10H2O}$. The molar mass of butane is approximately 58 g/mol, so 100 grams corresponds to about 1.72 moles of butane. Each mole of butane produces 4 moles of $\ce{CO2}$, hence $1.72 \times 4 = 6.88$ moles of $\ce{CO2}$. At STP (22.4 L/mol), $6.88 \times 22.4 \approx 154.2$ liters.

Correct answer: 22.5 grams

Correct answer: 22.5 grams. Explanation: The balanced equation is $\ce{2H2 + O2 -> 2H2O}$. Hydrogen (2 g/mol) gives $\frac{5.0}{2} = 2.5$ moles; oxygen (32 g/mol) gives $\frac{20.0}{32} = 0.625$ moles. Fully reacting the $\ce{H2}$ would need $\frac{2.5}{2} = 1.25$ moles of $\ce{O2}$, but only 0.625 moles are present, so $\ce{O2}$ is the limiting reagent. It produces $2 \times 0.625 = 1.25$ moles of $\ce{H2O}$, giving $1.25 \times 18 = 22.5$ grams of water.

Correct answer: 8.5 grams

Correct answer: 8.5 grams. Explanation: The balanced equation is $\ce{N2 + 3H2 -> 2NH3}$. Nitrogen (28 g/mol) gives $\frac{7.0}{28} = 0.25$ moles; hydrogen (2 g/mol) gives $\frac{3.0}{2} = 1.5$ moles. Reacting 0.25 mol $\ce{N2}$ needs 0.75 mol $\ce{H2}$, so nitrogen is the limiting reagent. The 1:2 ratio of $\ce{N2}$ to $\ce{NH3}$ gives 0.5 moles of ammonia, corresponding to $0.5 \times 17 = 8.5$ grams.

Correct answer: 22 grams

Correct answer: 22 grams. Explanation: The balanced chemical equation for the decomposition of calcium carbonate is $\ce{CaCO3 -> CaO + CO2}$. The molar mass of $\ce{CaCO3}$ is approximately 100 g/mol, so 50 grams corresponds to 0.5 moles. The molar mass of $\ce{CO2}$ is approximately 44 g/mol, hence $0.5 \times 44 = 22$ grams of $\ce{CO2}$ can be produced.

Correct answer: Cathode

Correct answer: Cathode. Explanation: In a galvanic cell, the reduction reaction always occurs at the cathode. This is where the reduction of ions takes place, gaining electrons.

Correct answer: Higher positive potential indicates a stronger oxidizing agent

Correct answer: Higher positive potential indicates a stronger oxidizing agent. Explanation: The more positive the standard electrode potential, the greater the tendency of the species to gain electrons and thus act as an oxidizing agent.

Correct answer: $\ce{H2 -> 2H+ + 2e-}$

Correct answer: $\ce{H2 -> 2H+ + 2e-}$. Explanation: The standard hydrogen electrode involves the oxidation of hydrogen gas into hydrogen ions, releasing electrons.

Correct answer: 6

Correct answer: 6. Explanation: In $\ce{K2Cr2O7}$, potassium has an oxidation state of +1 and oxygen has -2. Solving $2(+1) + 2(\mathrm{Cr}) + 7(-2) = 0$ gives chromium an oxidation state of +6.

Correct answer: $\ce{Mn}$

Correct answer: $\ce{Mn}$. Explanation: In the reaction, $\ce{MnO2}$ is reduced to $\ce{Mn}$, meaning manganese gains electrons (its oxidation state drops from +4 to 0).

Correct answer: 2

Correct answer: 2. Explanation: The reaction $\ce{Cu -> Cu^2+}$ involves the loss of two electrons, and each $\ce{Ag+}$ gains one electron to form $\ce{Ag}$. Overall, two electrons are transferred.

Correct answer: 5

The coefficient on $\ce{O2}$ is 5. Balancing the combustion of propane gives $\ce{C3H8 + 5O2 -> 3CO2 + 4H2O}$: the 3 carbons require 3 $\ce{CO2}$, the 8 hydrogens require 4 $\ce{H2O}$, and counting oxygen on the product side gives $(3 \times 2) + (4 \times 1) = 10$ oxygen atoms, which equals 5 $\ce{O2}$ molecules. To balance any equation you adjust coefficients (never subscripts) until every element has equal atom counts on both sides.