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Rationales 2026 Q&A | Instant
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1. Which subatomic particle has a positive electrical charge?
A. Electron
B. Neutron
C. Proton
D. Photon
Answer: C. Proton
Rationale: Protons carry a positive charge and are located in the nucleus of an
atom. Electrons are negatively charged, while neutrons have no charge.
2. The atomic number of an element is equal to the number of:
A. Neutrons
B. Electrons and neutrons
C. Protons
D. Nucleons
Answer: C. Protons
Rationale: The atomic number uniquely identifies an element and equals the
number of protons in its nucleus.
,3. Isotopes of the same element differ in the number of:
A. Protons
B. Electrons
C. Neutrons
D. Valence electrons
Answer: C. Neutrons
Rationale: Isotopes have the same number of protons but different numbers of
neutrons, resulting in different mass numbers.
4. Electrons occupy regions around the nucleus called:
A. Nucleons
B. Orbitals only
C. Electron clouds (orbitals)
D. Protons
Answer: C. Electron clouds (orbitals)
Rationale: Electrons are found in orbitals, which are regions of high probability
around the nucleus.
5. Which quantum number describes the principal energy level of an electron?
A. Magnetic quantum number
B. Spin quantum number
C. Azimuthal quantum number
D. Principal quantum number
Answer: D. Principal quantum number
Rationale: The principal quantum number (n) specifies the main energy level
occupied by an electron.
6. Which orbital has a spherical shape?
,A. p orbital
B. d orbital
C. f orbital
D. s orbital
Answer: D. s orbital
Rationale: The s orbital is spherical, whereas p orbitals are dumbbell-shaped.
7. According to the Aufbau principle, electrons fill orbitals:
A. Randomly
B. From highest to lowest energy
C. From lowest to highest energy
D. Based only on spin
Answer: C. From lowest to highest energy
Rationale: Electrons occupy the lowest-energy orbitals available before filling
higher-energy orbitals.
8. The Pauli exclusion principle states that an orbital can contain a maximum of:
A. One electron
B. Three electrons
C. Four electrons
D. Two electrons
Answer: D. Two electrons
Rationale: An orbital can hold two electrons with opposite spins.
9. Hund's rule states that electrons occupy equal-energy orbitals:
A. In pairs first
B. Randomly
, C. Singly before pairing
D. According to atomic mass
Answer: C. Singly before pairing
Rationale: Electrons fill degenerate orbitals singly with parallel spins before
pairing.
10. Elements in the same group of the periodic table have similar:
A. Atomic masses
B. Numbers of neutrons
C. Valence electron configurations
D. Numbers of isotopes
Answer: C. Valence electron configurations
Rationale: Similar valence electron arrangements give group members similar
chemical properties.
11. Atomic radius generally decreases across a period because:
A. Shielding increases greatly
B. Fewer protons are present
C. Effective nuclear charge increases
D. More neutrons are added
Answer: C. Effective nuclear charge increases
Rationale: Increased nuclear attraction pulls electrons closer to the nucleus across
a period.
12. Ionization energy generally increases across a period because:
A. Atomic radius increases
B. Shielding increases dramatically