23. Liquid A has vapor pressure x. Liquid B has vapor pressure y, and x>y.What is the mole fraction of A in the liquid mixture if the vapor above the solution is 30% A?
(A)0.3y/(0.7x+0.3y)
(B) 0.7y/(0.3x+0.7y)
(C) 0.3x/(0.3.xc+0.7y)
(D)0.7x/(0.7x+0.3y)
(E) none of these

19. Consider the following molecules.Ⅰ.BF3 Ⅱ.CHBr3 (C is the central atom.) III. Br2 IV. XeCl2 V. COVI. SF4 Select the molecule(s) that fit the given statement. These molecules have a zero net dipole moment. (A) III, V (B) III, IV (C) I, III, IV (D) III, IV, V (E) I, IIIL, IV, VI Il.

20. Which of the following is diamagnetic? (A) H2+ (B) C2+ (C) N2+ (D) N2 (E) F2+

21. Below is a phase diagram for compound X. You wish to purify a sample of X that was collected at P = 1.0 atm and T = 100 by subliming it. In order to sublime the sample, you should (A) increase P to 1.5 atm and then increase T'to 300 K. (B) increase T to 300 K, keeping P = 1.0 atm. (C) lower P to 0.5 atm and then increase T to 200 K. (D) increase T to 300 K and then lower P to 0.5 atm. (E) abandon the attempt to sublime X.

22. Alkali halides commonly have either the sodium chloride structure or the cesium chloride structure. The molar mass of CsCl is 2.88 times the molar mass of NaCl, and the edge length of the unit cell for NaCl is 1.37 times the edge length of the CsCl unit cell. Determine the ratio of the density of CsCl to the density of NaCl. (A) 0.541 (B) 0.984 (C) 1.02 (D) 1.85 (E) 2.10

24. The oxidation states of P in KPF6 is: (A)+1 (B)+3 (C)+5 (D)-3 (E) -5

25. Which of the following compounds is the strongest acid? (A) Acetic acid (B) Chloric acid (C) Hypochlorous acid (D) Boric acid (E) Chlorous acid

26. Which of the following ions has the lowest standard reduction potential? (A) Ag+ (B) Fe3+(C) Cr3+ (D) Mg2+  (E) Al3+

27. Which of the following names of ions is incorrect? (A) stannous: Sn2+ (B) plumbous: Pb2+ (C) ferric: Fe2+ (D) nitrate: NO3- (E) dichromate: Cr2O72-

28. The density of compound XHn as gas is 2.393 times that of O2. If 0.01 mol of this compound reacts with excess O2, 0.36 g of water is generated. The atomic weight of element X is: (A) 69.72 g/mol (B) 72.55 g/mol (C) 74.92 g/mol (D) 78.97 g/mol (E) 83.80 g/mol

29. Which of the following compound can be dissolved in water easily? (A) CsCl (B) AgCl (C) BaSO4 (D) CaF2 (E) MgCO3