68. Which of the following molecules has the smallest bond angle?
(A) CH₄
(B) SiH₄
(C) NH₃
(D) H₂O
(E) H₂S

64. What is the hybridization of the central carbon atom of allene (H2C=C=CH2)? (A) sp (B) sp2 (C) sp3 (D) dsp3 (E) d2 sp3

65. How many of the following molecules have all of their atoms in the same plane? H2C=CH2, H2C=C=CH2, CH3COCH3, NH3, CO2, BeCl2 (A) 2 (B) 3 (C) 4 (D) 5 (E) 6

66. Which of these species, , should be paramagnetic? (A) and (B) and O2 (C) O2 and (D) only O2 (E) All three are paramagnetic.

67. Based on the molecular orbital theory, which of the following molecules has the strongest bond? (A) (B) NO (C) (D) (E) All the above molecules have the same bond strength.

69. Which of the following statements is false? (A) The layering in a hexagonal closest-packed structure is aba. (B) A body-centered cubic unit cell has two atoms per unit cell. (C) For unit cells having the same edge length, a simple cubic structure would have a smaller density than a body-centered cube. (D) The size of tetrahedral hole is always larger than the size of octahedral hole. (E) Atoms in a solid, consisting of only one element would have six nearest neighbors if the crystal structure was a simple cubic array.

70. Rank the following compounds in the order from the highest boiling point to the lowest boiling point. (a) C2H5OC2H5 (b) CH3OH (c) HCONH2 (d) HCOOH (A) (b) ＞ (a) ＞ (c) ＞ (d) (B) (b) ＞ (a) ＞ (d) ＞ (c) (C) (c) ＞ (d) ＞ (b) ＞ (a) (D) (d) ＞ (c) ＞ (b) ＞ (a) (E) (b) ＞ (d) ＞ (a) ＞ (c)

71. The reaction “A + 2B → 2 C” exhibits the rate law as following: Rate = k [A][B] 2 Which of the following mechanisms could be consistent with this rate law? (A) A + 2B → D (fast), D → 2 C (slow) (B) 2B → D (fast), D + A → 2 C (slow) (C) 2B → D (slow), A + D → E (fast), E → 2 C (fast) (D) A + B ⇌ D (fast equilibrium), B + D → 2 C (slow) (E) B ⇌ 2 D (fast equilibrium), D + A → C (slow)

72. Consider the following reaction: N2(g) + 3 H2(g) ⇌ 2 NH3(g), equilibrium constant (K) = Predict the reaction direction of the following cases: (A) a. No shift； b. shift to left； c. shift to right (B) a. No shift； b. shift to right； c. shift to left (C) a. Shift to right； b. shift to left； c. no shift (D) a. Shift to left； b. shift to right； c. shift to right (E) a. Shift to left； b. shift to right； c. shift to left

73. Consider the following reaction at equilibrium. Which change will cause the equilibrium to shift to the left?  2NOBr(g) ⇌ 2NO(g) + Br2(g), = +30 kJ/mol (A) Increase the container volume (B) Remove some NO (C) Decrease the temperature (D) Add more NOBr (E) Increase the temperature

74. How many of the following will raise the pH of a weak acid HA in aqueous solution?I. Addition of water.II. Making a buffered solution by adding NaA(s).III. Addition of NaCl(s).IV. Addition of HNO3.V. Titrating with KOH.(A) 5 (B) 4 (C) 3 (D) 2 (E) 1