31. Doping Se with As would produce a(n)_____semiconductor with_____conductivity compared to pure Se.
(A) n-type, increased
(B) p-type, increased
(C) n-type, decreased
(D) intrinsic, identical
(E) p-type, decreased

27. What type of structure does the XeOF2 molecule have? (A) trigonal planar (B) octahedral (C) pyramidal (D) T-shaped (E) tetrahedral

28. Which of the following statements is false? (A) The carbon-carbon bond inis shorter than the one in CH3CH3 (B) the carbon-carbon bond in is stronger than the one in CH3CH3 (C) C2 is diamagnetic (D) C2 is paramagnetic (E) two of these statements are false.

29. Consider the molecular-orbital energy-level diagrams for O2 and NO. Which of the following is true?I : Both molecules are paramagnetic； II: The bond strength of O2 is greater than the bond strength of NO； III: NO is an example of a homonuclear diatomic molecule； IV: The ionization energy of NO is smaller than the ionization energy of NO+ . (A) I and II only (B)I, II, and IV (C) I and IV (D) II and III (E) I only

30. How many ofthe following are paramagnetic?(A) 3 (B) 2 (C) 4 (D) 5(E) 0

32. Which of the following statements is incorrect? (A) ionic solids have high melting points (B) the binding forces in a molecular solid include London dispersion forces (C) ionic solids are insulators (D) molecular solids have high metting points (E) all of these statements are correct.

33. A liquid placed in a closed container will evaporate until equilibrium is reached. At equilibrium, which of the following statements is not true? (A) liquid molecules are still evaporating (B) the number of vapor molecules remains essentially constant (C) the partial pressure exerted by the vapor molecules is called the vapor pressure of the liquid (D) the boundary (meniscus) between the liquid and the vapor disappears (E) all of these statements are true.

34. How many different possible tetramethylbenzenes exist? (A) 6 (B)2 (C) 5 (D)3(E)4

35. Oxidation of a primary alcohol results in a(n)_____， and oxidation of a secondary alcohol results in a(n)_____. (A) ester, ether (B) ketone, aldehyde (C) amine, carboxylic acid (D) carboxylic acid, amine (E) aldehyde, ketone

36. Choose the correct molecular structure for .(A) octahedral (B) tetrahedral (C) trigonal planar (D) trigonal bipyramidal (E) linear

37. What Group 6A elements are semiconductors? (A) selenium and polonium (B) sulfur and tellurium (C) sulfur and selenium (D) selenium and tellurium (E) tellurium and polonium