ACS Chemistry General Exam 2026 Questions with Correct Answers and Explanations

ACS Chemistry General Exam 2026 Questions
with Correct Answers and Explanations

Q1: Which particle determines the identity of an element?

 A) Electron
 B) Neutron
 C) Proton
 D) Nucleus

Correct Answer: C) Proton

Explanation: The number of protons in an atom's nucleus defines the atomic number,
which uniquely identifies an element. Changing the number of protons changes the
element itself, while electrons and neutrons can vary without altering elemental identity.

Q2: What is the electron configuration of oxygen (Z = 8)?

 A) 1s² 2s² 2p⁴
 B) 1s² 2s² 2p⁶
 C) 1s² 2p⁶
 D) 1s² 2s² 2p³

Correct Answer: A) 1s² 2s² 2p⁴

Explanation: Oxygen has 8 electrons. Filling orbitals in order gives 1s² (2 electrons), 2s² (2
electrons), and 2p⁴ (4 electrons). This configuration reflects Hund's rule and the Aufbau
principle.

Q3: Which quantum number determines the shape of an orbital?

 A) n (principal)
 B) l (angular momentum)
 C) mₗ (magnetic)
 D) mₛ (spin)

Correct Answer: B) l (angular momentum)

, *Explanation: The angular momentum quantum number (l) determines the shape of an
orbital. l = 0 corresponds to s orbitals (spherical), l = 1 to p orbitals (dumbbell-shaped),
and higher values to more complex shapes.*

Q4: Which element has the largest atomic radius?

 A) Na
 B) Cl
 C) F
 D) O

Correct Answer: A) Na

Explanation: Atomic radius increases down a group and decreases across a period. Sodium
(Na) is lower and to the left compared to the other elements listed, meaning it has more
electron shells and less effective nuclear charge pulling electrons inward, giving it the
largest radius.

Q5: What is the charge of an electron?

 A) +1
 B) -1
 C) 0
 D) +2

Correct Answer: B) -1

*Explanation: Electrons carry a fundamental negative charge of -1. This is a basic fact of
atomic structure that governs chemical bonding and electricity.*


Chemical Bonding & Molecular Geometry (Questions 6-10)
Q6: Which bond is most polar?

 A) C–H
 B) O–H
 C) N–H
 D) C–C

Correct Answer: B) O–H

, Explanation: Bond polarity depends on electronegativity difference. Oxygen (3.44) is much
more electronegative than hydrogen (2.20), creating a strong dipole. Other bonds listed
have smaller electronegativity differences and are less polar.

Q7: What is the shape of CO₂?

 A) Bent
 B) Linear
 C) Trigonal planar
 D) Tetrahedral

Correct Answer: B) Linear

Explanation: CO₂ has two electron domains around the central carbon atom, leading to a
linear geometry with a 180° bond angle. There are no lone pairs on the central atom to
cause bending.

Q8: Which compound exhibits hydrogen bonding?

 A) CH₄
 B) NH₃
 C) CO₂
 D) H₂

Correct Answer: B) NH₃

Explanation: Hydrogen bonding occurs when hydrogen is bonded to highly electronegative
atoms like N, O, or F. NH₃ contains N–H bonds, allowing hydrogen bonding. CH₄ and H₂
lack polarity, and CO₂ is linear and nonpolar.

Q9: Which is an ionic bond?

 A) H₂
 B) CO₂
 C) NaCl
 D) CH₄

Correct Answer: C) NaCl

, Explanation: Ionic bonds form between metals and nonmetals through electron transfer.
Sodium (metal) transfers an electron to chlorine (nonmetal), creating Na⁺ and Cl⁻ ions that
are held together by electrostatic attraction.

Q10: Which intermolecular force is strongest?

 A) London dispersion
 B) Dipole-dipole
 C) Hydrogen bonding
 D) Ion-dipole

Correct Answer: D) Ion-dipole

Explanation: Ion-dipole forces involve full charges (from ions) interacting with partial
charges (from polar molecules), making them stronger than other intermolecular forces
listed. These are especially important in solutions of ionic compounds in polar solvents like
water.


Stoichiometry & Mole Calculations (Questions 11-15)
Q11: What is the molar mass of CO₂?

 A) 28 g/mol
 B) 32 g/mol
 C) 44 g/mol
 D) 46 g/mol

Correct Answer: C) 44 g/mol

*Explanation: Molar mass is the sum of atomic masses. Carbon = 12 g/mol + Oxygen (16
× 2 = 32 g/mol) = 44 g/mol total.*

Q12: What is Avogadro's number?

 A) 6.02 × 10²³
 B) 3.01 × 10²³
 C) 1.00 × 10²³
 D) 9.11 × 10⁻³¹

Correct Answer: A) 6.02 × 10²³