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

60. MRI machine probes the concentration distribution of water molecules by detecting the magnetic resonance between the nucleus of hydrogen atoms, placed in a strong static magnetic field B, and a small alternating magnetic field of frequency f. If B is 2T and the z-component of the proton magnetic moment is J/T. What is the frequency f of the alternating magnetic field? (Plank constant is J/s) (A) 43 MHz (B) 85 MHz (C) 170 MHz (D) 340 MHz (E) 680 MHz

61. When a certain atom emits a photon of light at 232 nm, what is the frequency of this light? (A) (B) (C) (D) (E) None of the above.

62. Given a cylinder of fixed volume filled with 1 mol of argon gas, which of the following is correct? (Assume all gases obey the ideal gas law.) (A) If the temperature of the cylinder is changed from 25°C to 50°C, the pressure inside the cylinder will remain the same. (B) If a second mole of argon is added to the cylinder, the ratio of T/P would decrease. (C) A cylinder of identical volume filled with the same pressure of helium must contain more atoms of gas, because helium has a smaller atomic radius than argon. (D) Two of the above. (E) None of the above.

63. Which of the following statements is true? (A) The energy of electromagnetic radiation increases as its frequency decreases. (B) An electron in the n = 4 state in the hydrogen atom can go to the n = 2 state by absorbing electromagnetic radiation at the appropriate frequency. (C) The frequency and wavelength of electromagnetic radiation are proportional to each other. (D) The energy of an atom is increased when electromagnetic radiation is emitted from it. (E) An excited atom can return to its ground state by emitting electromagnetic radiation.

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.

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

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)