23. How many of the following molecules have all of their atoms in the same plane? H₂C = CH₂, F₂O, H₂CO,NH₃, CO₂, BeC₂ and H₂O₂
(A) 4
(B) 5
(C) 6
(D) 7
(E) 3

19. How many unpaired electr rons does cobalt have in its ground state? (A) 7 (B) 27 (C) 5 (D)3 (E)1

20. Which of the following exhibits the correct orders (increasing) for atomic radius and ionization energy, respectively? (A) F, S, O, and O, S, F (B) F, O, s, and s, O, F (C) s, O, F, and F, O, s (D) S, F, O, and S, F, O (E) none of these

21. Draw the Lewis structures of the molecules below, and use them to answer the following questions. How many of the molecules have no dipole moment? BH3, NO2, SF6, O3 and PCl5 (A) 2 (B) 4 (C) 1 (D) 3 (E) they are all polar.

22. How many of the following molecules and ions are linear? (A) 4 (B) 2 (C) 3 (D) 1 (E)0

24. Which of the following statements about the ion is false? (A) the ion has a total of 24 electrons (B) the orbitals on the carbon atom are sp2 hybridized (C) the ion is expected to be diamagnetic (D) one C-O bond is shorter than the others (E) it has a planar molecular geometry

25. An ethyl group that is attached to a substituent that does not contain a hydrogen atom appears as what in a NMR spectrum? (A) a triplet and a quartet with relative intensities of 3 and 2, respectively (B) a triplet and a quartet with relative intensities of 2 and 3, respectively (C) a doublet and a triplet with relative intensities of 2 and 3, respectively (D) a doublet and a triplet with relative intensities of 3 and 2, respectively (E) none of these

26. How many of the following has a bond order = 0.5? (A) 2(B) 3 (C)4 (D) 1 (E)0

27.In the unit cell of sphalerite, ions occupy half the tetrahedral holes in a face-centered cubic lattice ions. What is the number of formula units of ZnS in the unit cell? (A) 3 (B) 5 (C) 4 (D) 1 (E) 2

28. Which of the compounds below is an example of a network solid? (A) NaCl(s) (B) S8(s) (C) MgO(s) (D) SiO2(S) (E)

29. A certain substance, X, has a triple-point temperature of 20℃ at a pressure of 2.0 atm. Which one of the following statements cannot possibly be true? (A) X can exist as a liquid above 20℃  (B) both liquid and solid X have the same vapor pressure at 20℃ (C) liquid X can exist as a stable phase at 25℃ , 1 atm (D) X can exist as a solid above 20℃  (E) all of these statements could be true