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.

24. The valence electron configuration of an element is . To which group does X belong? (A) Group 3A (B) Group 4A (C) Group 6A (D) Group 5A (E) Group 7A

25. The_______ states that in a given atom no two electrons can have the same set of four quantum numbers (n, I, mI, ms). (A) Pauli exclusion principle (B) Huygens-Fresnel principle (C) Cauchy's argument principle (D) Heisenberg uncertainty principle(E) Le Chatelier's principle

26. Of the following, which molecule has the smallest bond angle? (A)CO2(B) H2O (C) SCI2 (D) SO3 (E) NF3

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

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

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

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