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.

17. Which of the following statements is/are true of the electrolysis of brine? I: chlorine is produced at the anode of the cell during the electrolysis of brine；Il: under normal circumstances, sodium is produced at the cathode of the cell during the electrolysis of brine； III: hydrogen is produced at the cathode of the cell during the electrolysis of brine. (A) I only (B) II only (C) III only (D) I and II (E) I and Ill

18. How many f orbitals have the value n = 3? (A) 3(B) 1 (C)0(D) 5(E)7

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

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

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

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