24. Naturally occurring copper exists in two isotopic forms: ⁶³Cu and ⁶⁵Cu. The atomic mass of copper is 63.55 amu. What is the approximate natural abundance of ⁶³Cu?
(A) 63%
(B) 90%
(C) 80%
(D) 85%
(E) 72%

20. Which of the following does NOT contain at least one pi bond? (A) H2CO (B) CO2 (C) C2H2 (D) NO (E) All of the above (A-D) contain at least one pi bond.

21. Order the intermolecular forces (dipole-dipole, London dispersion, ionic, and hydrogen-bonding) from weakest to strongest. (A) dipole-dipole, London dispersion, ionic, and hydrogen-bonding (B) London dispersion, dipole-dipole, hydrogen-bonding, and ionic (C) hydrogen-bonding, dipole-dipole, London dispersion, and ionic (D) dipole-dipole, ionic, London dispersion, and hydrogen-bonding (E) London dispersion, ionic, dipole-dipole, and hydrogen-bonding

22. Which separation technique is based on differences in the affinity of the substances to be separated? (A) filtration (B) distillation (C) solvent extraction (D) paper chromatography (E) None of the above.

23. Which of the following gives correct rank of the ionization energies for Cs, Na, O, F, and S? (A) Cs ＜ Na ＜ S ＜ O ＜ F (B) Cs ＜ S ＜ Na ＜ O ＜ F (C) F ＜ O ＜ Na ＜S ＜ Cs (D) F ＜ O ＜ S ＜ Na ＜ Cs (E) Na ＜ S ＜ Cs ＜ F ＜ O

25. The correct mathematical expression for finding the molar solubility(s) of Al(OH)3 is . (A) 9 s2 = Ksp (B) 3 s3 = Ksp (C) 27 s4 = Ksp (D) s4 = Ksp (E) 9 s3 = Ksp

26. Consider the following octahedral complex structures, each involving ethylene diamine and two different, unidentate ligands X and Y. Which, if any, of the following pairs are optical isomers? (A) 1 and 4 (B) 1 and 2 (C) 3 and 4 (D) 1 and 3 (E) None of the above.

27. For which of the following processes would ∆S° be expected to be most positive? (A) NH3(g) + HCl(g) → NH4Cl(g) (B) 2NH4NO3(s) → 2N2(g) + O2(g) + 4H2O(g) (C) H2O(l) → H2O(s) (D) N2O4(g) → 2NO2(g) (E) O2(g) + 2H2(g) → 2H2O(g)

28. Why is this reaction considered to be exothermic? (A) Because energy difference A and energy difference C are about equal. (B) Because energy difference B is greater than energy difference C plus energy difference A. (C) Because energy difference A is greater than energy difference C. (D) Because energy difference B is greater than energy difference A. (E) Because energy difference B is greater than energy difference C.

29. The structure of pentose is shown on the down figure. How many carbon atoms with chirality are there in this molecule? (A) 1 (B) 2 (C) 3 (D) 4 (E) 5

30. Which one is Bragg equation? (A) F = ma (B) Hɸ = Eɸ (C) nλ = 2dsinθ (D) Δx ∙ Δp = h (E) E = mc2