21. Determine, respectively, the proper formulas for sodium tetrachloroaluminate(III) and sodium tetrachlorocobaltate(II).
(A) Na(AlCl₄)； Na₂(CoCl₄)
(B) Na(AlCl₄)； Na(CoCl₄)
(C) Na₂(AlCl₄)； Na(CoCl₄)
(D) Na₂(AlCl₄)； Na₂(CoCl₄)
(E) Na₃(AlCl₄)； Na₂(CoCl₄)

17. How many nanometers is equal to 7.6 meters? (A) 76 × 107 (B) 76 × 108 (C) 76 × 109 (D) (E)

18. A specific type of nucleus has a half-life of 40 min. How long is required for 80% of the nuclides to decompose? (ln2 = 0.693； ln0.2 = -1.609) (A) 80 min (B) 85 min (C) 95 min (D) 102 min (E) 120 min

19. Which of the following ionic compounds has the largest lattice energy (i.e., the lattice energy most favorable to a stable lattice)? (A) MgO (B) CaO (C) Li2O (D) Na2O (E) K2O

20. Determine the hybridization of Cl in . (A) sp (B) sp2 (C) sp3 (D) dsp3 (E) d2sp3

22. What is the sum of all coefficients when the following equation is balanced? NH3(g) + O2(g) → NO2(g) + H2O(g) (A) 6 (B) 14 (C) 17 (D) 21 (E) 23

23. A compound is composed of element X and hydrogen. A mass analysis shows the compound contains 82.35% of X, with three times as many hydrogen atoms as X atoms per molecule. Which element is X? (atomic mass: B = 10.81, C = 12.01, N = 14.01, Al = 26.98, P = 30.97) (A) B (B) C (C) N (D) Al (E) P

24. Which of the following statements is incorrect? (A) Heteronuclear linear molecules can have a net dipole moment. (B) A molecular dipormenant is the dipole moment of the molecular taken as a whole. (C) Ionic bonding results from the transfer of electrons from one atom to another. (D) A molecule with polar bonds must be polar. (E) The distribution of electrons in a polar bond is closer to the more electronegative element.

25. Regarding to the concept of reduction and oxidation, which of the following statements is true? (A) All chemical changes is accompanied by reduction and oxidation. (B) When the atom is oxidized, the size becomes larger. (C) The oxidizing agent is electron donor. (D) Reduction and oxidation can occur independently of each other. (E) Reduction and oxidation describe the gain and loss of electron(s), respectively.

26. You have immersed electrodes of a light bulb in a solution of H2SO4 such that the light bulb is on. You add a dilute solution and the bulb grows dim. Which of the following molecule could be in the solution? (A) Cu(NO3)2 (B) K2SO4 (C) NaNO3 (D) ZnCl2 (E) Pb(NO3)2

27. Which of the following anions is the most basic? (A) (B) (C) (D) (E)