1. Which set of quantum numbers is not allowed for
any electron in an atom?
A. (n = 2, l = 1, mₗ = –1, mₛ = +½)
B. (n = 3, l = 2, mₗ = +2, mₛ = –½)
C. (n = 4, l = 0, mₗ = 0, mₛ = +1)
D. (n = 1, l = 0, mₗ = 0, mₛ = –½)
o Answer: C
o Rationale: The spin quantum number mₛ can
only be +½ or –½; +1 is forbidden (Chemistry
LibreTexts).
2. What is the electron configuration of Fe³⁺?
A. [Ar] 3d⁶
B. [Ar] 3d⁵
C. [Ar] 4s² 3d³
D. [Ar] 4s¹ 3d⁵
o Answer: B
o Rationale: Fe (Z = 26) is [Ar] 4s² 3d⁶; removing
three electrons removes both 4s and one 3d: [Ar]
3d⁵ (Chemistry LibreTexts).
3. Across period 3 (Na → Ar), which property
generally _______?
(a) atomic radius decreases
(b) first ionization energy increases
A. both (a) and (b)
B. (a) only
, C. (b) only
D. neither
o Answer: A
o Rationale: Increasing nuclear charge pulls
electrons in tighter (smaller radii) and makes
removal harder (higher I₁) (Chemistry
LibreTexts).
4. Which element has the highest electronegativity?
A. Na
B. Mg
C. Al
D. Cl
o Answer: D
o Rationale: Electronegativity increases across a
period, peaking at halogens (Cl) (Chemistry
LibreTexts).
5. The effective nuclear charge (Z_eff) felt by a
valence electron _______ across a period.
A. increases
B. decreases
C. remains constant
D. first increases then decreases
o Answer: A
o Rationale: Core electrons shield imperfectly; as
Z increases with constant shielding, Z_eff rises
(Chemistry LibreTexts).
, 2. Chemical Bonding & Intermolecular Forces (5
Questions)
Key Reference: Fundamentals of chemical bonding
(Chemistry LibreTexts)
6. Which bond is most polar?
A. C–H
B. C–Cl
C. C–O
D. C–F
o Answer: D
o Rationale: Greater electronegativity difference →
more polar; F–C difference is largest (Wikipedia).
7. A molecule with formula AX₂E₂ (VSEPR) is
______.
A. linear
B. trigonal planar
C. bent (< 120°)
D. tetrahedral
o Answer: C
o Rationale: Two bonds and two lone pairs on
central atom → bent geometry, bond angle ≈
104° (Chemistry LibreTexts).
8. Which has the highest boiling point?
A. CH₄
any electron in an atom?
A. (n = 2, l = 1, mₗ = –1, mₛ = +½)
B. (n = 3, l = 2, mₗ = +2, mₛ = –½)
C. (n = 4, l = 0, mₗ = 0, mₛ = +1)
D. (n = 1, l = 0, mₗ = 0, mₛ = –½)
o Answer: C
o Rationale: The spin quantum number mₛ can
only be +½ or –½; +1 is forbidden (Chemistry
LibreTexts).
2. What is the electron configuration of Fe³⁺?
A. [Ar] 3d⁶
B. [Ar] 3d⁵
C. [Ar] 4s² 3d³
D. [Ar] 4s¹ 3d⁵
o Answer: B
o Rationale: Fe (Z = 26) is [Ar] 4s² 3d⁶; removing
three electrons removes both 4s and one 3d: [Ar]
3d⁵ (Chemistry LibreTexts).
3. Across period 3 (Na → Ar), which property
generally _______?
(a) atomic radius decreases
(b) first ionization energy increases
A. both (a) and (b)
B. (a) only
, C. (b) only
D. neither
o Answer: A
o Rationale: Increasing nuclear charge pulls
electrons in tighter (smaller radii) and makes
removal harder (higher I₁) (Chemistry
LibreTexts).
4. Which element has the highest electronegativity?
A. Na
B. Mg
C. Al
D. Cl
o Answer: D
o Rationale: Electronegativity increases across a
period, peaking at halogens (Cl) (Chemistry
LibreTexts).
5. The effective nuclear charge (Z_eff) felt by a
valence electron _______ across a period.
A. increases
B. decreases
C. remains constant
D. first increases then decreases
o Answer: A
o Rationale: Core electrons shield imperfectly; as
Z increases with constant shielding, Z_eff rises
(Chemistry LibreTexts).
, 2. Chemical Bonding & Intermolecular Forces (5
Questions)
Key Reference: Fundamentals of chemical bonding
(Chemistry LibreTexts)
6. Which bond is most polar?
A. C–H
B. C–Cl
C. C–O
D. C–F
o Answer: D
o Rationale: Greater electronegativity difference →
more polar; F–C difference is largest (Wikipedia).
7. A molecule with formula AX₂E₂ (VSEPR) is
______.
A. linear
B. trigonal planar
C. bent (< 120°)
D. tetrahedral
o Answer: C
o Rationale: Two bonds and two lone pairs on
central atom → bent geometry, bond angle ≈
104° (Chemistry LibreTexts).
8. Which has the highest boiling point?
A. CH₄
