ACS CHEMISTRY GENERAL EXAM 2026 COMPLETE 250
QUESTIONS AND ANSWERS WITH RATIONALES |
GRADED A+ | 2026/2027 UPDATE | 100% VERIFIED
SOLUTIONS
EXAM STRUCTURE OVERVIEW
Content Area Topics Covered
Atomic Structure Atomic theory, quantum mechanics, orbitals, electron configuratio
Molecular Structure & Bonding Bond types, VSEPR theory, Lewis structures, molecular orbitals
Stoichiometry Mole concept, limiting reagent, percent yield, empirical formulas
States of Matter/Solutions Gas laws, phase diagrams, colligative properties, molarity
Thermodynamics Enthalpy, entropy, Gibbs free energy, calorimetry
Kinetics Rate laws, reaction order, Arrhenius equation, catalysis
Equilibrium Equilibrium constants, Le Chatelier's principle, Ksp
Acids & Bases pH, buffers, titration, acid-base equilibrium
Electrochemistry Redox reactions, galvanic cells, Nernst equation
Nuclear Chemistry Radioactive decay, half-life, nuclear reactions
SECTION 1: ATOMIC STRUCTURE & PERIODIC TRENDS (Questions 1–50)
,Question 1
Which subatomic particle determines the identity of an element?
A) Electron
B) Neutron
C) Proton
D) Nucleus
Correct Answer: C) Proton
Rationale: The number of protons in an atom's nucleus is the atomic number, which
uniquely identifies the element. Changing the number of protons changes the element
itself; electrons and neutrons can vary without altering elemental identity .
Question 2
How many protons, neutrons, and electrons are in an atom of ⁵⁶Fe?
A) 26, 30, 26
B) 26, 56, 26
C) 30, 26, 26
D) 56, 26, 26
Correct Answer: A) 26, 30, 26
Rationale: The atomic number of iron is 26 (protons = 26). Mass number = 56, so neutrons
= 56 – 26 = 30. In a neutral atom, electrons = protons = 26 .
Question 3
Isotopes of the same element differ in the number of:
A) Protons
B) Electrons
C) Neutrons
D) Nucleons
Correct Answer: C) Neutrons
,Rationale: Isotopes are atoms with the same number of protons but different numbers of
neutrons. They have the same atomic number but different mass numbers .
Question 4
Which particle, if lost from the nucleus, would NOT change the atomic number?
A) Alpha particle
B) Neutron
C) Proton
D) Electron
Correct Answer: B) Neutron
Rationale: The atomic number is determined by the number of protons. Losing a neutron
changes the mass number (creating an isotope) but does not change the element's
identity. Losing an alpha particle (2 protons, 2 neutrons) or a proton would change the
atomic number .
Question 5
Which of the following elements has the highest ionization energy?
A) Na
B) Mg
C) Al
D) Ne
Correct Answer: D) Ne
Rationale: Ionization energy increases across a period and decreases down a group. Neon
is at the far right of period 2 and has a very high ionization energy due to its full octet
(noble gas configuration) .
Question 6
Arrange the following atoms in order of increasing atomic radius: F, O, C, Li.
, A) Li < C < O < F
B) F < O < C < Li
C) C < O < F < Li
D) Li < O < C < F
Correct Answer: B) F < O < C < Li
Rationale: Atomic radius decreases from left to right across a period. Li (largest) → C → O
→ F (smallest). So F < O < C < Li .
Question 7
Which of the following has the largest ionic radius?
A) Na⁺
B) Mg²⁺
C) Al³⁺
D) O²⁻
Correct Answer: D) O²⁻
Rationale: O²⁻ has gained two electrons, increasing electron-electron repulsion and
expanding the radius, making it significantly larger than any of the cations listed. Cations
are smaller than their parent atoms; anions are larger .
Question 8
The element with the highest electronegativity is:
A) Francium
B) Oxygen
C) Fluorine
D) Chlorine
Correct Answer: C) Fluorine
Rationale: Fluorine (4.0 on the Pauling scale) is the most electronegative element.
Electronegativity generally increases from left to right and decreases down a group .
QUESTIONS AND ANSWERS WITH RATIONALES |
GRADED A+ | 2026/2027 UPDATE | 100% VERIFIED
SOLUTIONS
EXAM STRUCTURE OVERVIEW
Content Area Topics Covered
Atomic Structure Atomic theory, quantum mechanics, orbitals, electron configuratio
Molecular Structure & Bonding Bond types, VSEPR theory, Lewis structures, molecular orbitals
Stoichiometry Mole concept, limiting reagent, percent yield, empirical formulas
States of Matter/Solutions Gas laws, phase diagrams, colligative properties, molarity
Thermodynamics Enthalpy, entropy, Gibbs free energy, calorimetry
Kinetics Rate laws, reaction order, Arrhenius equation, catalysis
Equilibrium Equilibrium constants, Le Chatelier's principle, Ksp
Acids & Bases pH, buffers, titration, acid-base equilibrium
Electrochemistry Redox reactions, galvanic cells, Nernst equation
Nuclear Chemistry Radioactive decay, half-life, nuclear reactions
SECTION 1: ATOMIC STRUCTURE & PERIODIC TRENDS (Questions 1–50)
,Question 1
Which subatomic particle determines the identity of an element?
A) Electron
B) Neutron
C) Proton
D) Nucleus
Correct Answer: C) Proton
Rationale: The number of protons in an atom's nucleus is the atomic number, which
uniquely identifies the element. Changing the number of protons changes the element
itself; electrons and neutrons can vary without altering elemental identity .
Question 2
How many protons, neutrons, and electrons are in an atom of ⁵⁶Fe?
A) 26, 30, 26
B) 26, 56, 26
C) 30, 26, 26
D) 56, 26, 26
Correct Answer: A) 26, 30, 26
Rationale: The atomic number of iron is 26 (protons = 26). Mass number = 56, so neutrons
= 56 – 26 = 30. In a neutral atom, electrons = protons = 26 .
Question 3
Isotopes of the same element differ in the number of:
A) Protons
B) Electrons
C) Neutrons
D) Nucleons
Correct Answer: C) Neutrons
,Rationale: Isotopes are atoms with the same number of protons but different numbers of
neutrons. They have the same atomic number but different mass numbers .
Question 4
Which particle, if lost from the nucleus, would NOT change the atomic number?
A) Alpha particle
B) Neutron
C) Proton
D) Electron
Correct Answer: B) Neutron
Rationale: The atomic number is determined by the number of protons. Losing a neutron
changes the mass number (creating an isotope) but does not change the element's
identity. Losing an alpha particle (2 protons, 2 neutrons) or a proton would change the
atomic number .
Question 5
Which of the following elements has the highest ionization energy?
A) Na
B) Mg
C) Al
D) Ne
Correct Answer: D) Ne
Rationale: Ionization energy increases across a period and decreases down a group. Neon
is at the far right of period 2 and has a very high ionization energy due to its full octet
(noble gas configuration) .
Question 6
Arrange the following atoms in order of increasing atomic radius: F, O, C, Li.
, A) Li < C < O < F
B) F < O < C < Li
C) C < O < F < Li
D) Li < O < C < F
Correct Answer: B) F < O < C < Li
Rationale: Atomic radius decreases from left to right across a period. Li (largest) → C → O
→ F (smallest). So F < O < C < Li .
Question 7
Which of the following has the largest ionic radius?
A) Na⁺
B) Mg²⁺
C) Al³⁺
D) O²⁻
Correct Answer: D) O²⁻
Rationale: O²⁻ has gained two electrons, increasing electron-electron repulsion and
expanding the radius, making it significantly larger than any of the cations listed. Cations
are smaller than their parent atoms; anions are larger .
Question 8
The element with the highest electronegativity is:
A) Francium
B) Oxygen
C) Fluorine
D) Chlorine
Correct Answer: C) Fluorine
Rationale: Fluorine (4.0 on the Pauling scale) is the most electronegative element.
Electronegativity generally increases from left to right and decreases down a group .
