15. A mineral crystallizes in a cubic closest-packed array of oxygen ions (O²⁻) with aluminum ions (Al³⁺) in some of the octahedral holes and magnesium ions (Mg²⁺) in some of the tetrahedral holes. Which of the following statements about this compound is correct?
(A) The empirical formula is Al₂Mg₂O₅.
(B) Half of the octahedral holes are filled with aluminum ions.
(C) One-fourth of the tetrahedral holes are filled with magnesium ions.
(D) There are two oxygen ions in a unit cell.
(E) There are four aluminum ions in a unit cell.

11. Which of the available number of stereoisomers for the following open-chain monosaccharide is correct? (A) aldopentose: 8 stereoisomers (B) aldohexose: 32 stereoisomers (C) ketotetrose: 4 stereoisomers (D) aldotriose: 4 stereoisomers (E) ketohexose: 16 stereoisomers

12. Which of the following forms of peptide residues is the most basic?  (A)(B)(C)(D)(E)

13. Which of the following statements about nuclear reaction and stability is correct? (Z is the atomic number.) (A) As Z increases, nuclides need a smaller neutron-to-proton ratio for stability. (B) Nuclides with small Z values are often observed to be a-particle producers. (C) A radioactive nuclide that decays from 2.00 × 1010 atoms to 2.50 × 10º atoms in 30.0 min has a half-life of 15.0 min. (D) Both the radioactive processes of positron production and electron capture increase the neutron-to-proton ratio. (E) If less than one neutron from each fission event causes another fission event, the fission situation is described as supercritical.

14. What is the major product for following reaction? (A)(B)(C)(D)(E)

16. Two moles of a monatomic ideal gas were heated at a constant pressure of 1 atm from 200 K to 300 K. The entropy (S°) for this gas at 200 K is 6.00 J mol⁻¹ K⁻¹. Regarding the related thermodynamic parameters during the process, which of the following statements is correct? (R = 8.31 J mol⁻¹ K⁻¹; ln2 = 0.69; ln3 = 1.10) (A) internal energy change (ΔE) = 1662 J (B) work (w) = -831 J (C) heat (q) = 2493 J (D) the entropy change (ΔS) = 8.52 J K⁻¹ (E) the entropy (S°) for this gas at 300 K is 14.52 J mol⁻¹ K⁻¹

17. Which of the following compounds (A-E) is not aromatic?  (A) A (B) B (C) C (D) D (E) E

18. Titrating 30.00 mL of a saturated calcium iodate solution requires 27.00 mL of a 0.100 M solution of Na₂S₂O₃ according to the equation IO₃⁻ + S₂O₃²⁻ + H⁺ → I⁻ + S₄O₆²⁻ + H₂O (not balanced) What is the Ksp for Ca(IO₃)₂? (A) 7.14 × 10⁻⁸ (B) 1.68 × 10⁻⁶ (D) 4.62 × 10⁻⁴ (E) 6.23 × 10⁻² (C) 2.79 × 10⁻⁵

19. In an organic solution, an organometallic compound R3MPH3 (R = alkyl, M = metal) decomposes into a hydrocarbon R-R and a new compound RMPH3. The mechanism for the reaction was proposed as follows. The first and third steps are fast, whereas the second step is slow. What is the rate law based on the mechanism? (A) Rate =(k1k3/k-1)R3MPH3[PH3] (B) Rate = R-R/[R3M] (C) Rate = (k2k1/k-1)[R3MPH3]/[PH3] (D) Rate = k2[R3M]/[PH3] (E) Rate = k1[R3MPH3]

20. The heat required to raise the temperature from 298 K to 398 K for 2 moles of a gas at constant volume is 4155 J. At constant pressure, the internal energy required to heat the same gas from 450 K to 550 K is 4960 J, and the gas does 857 J of work during this expansion. Which of the following statements is correct? (R = 8.31 J mol⁻¹ K⁻¹) (A) This gas is monatomic. (B) This gas is not an ideal gas. (C) The molar heat capacity at constant volume is 41.55 J mol⁻¹ K⁻1. (D) The molar heat capacity at constant pressure is 49.60 J mol⁻¹ K⁻1. (E) The internal energy change is 2078 J when the gas is heated from 273 K to323 K at constant pressure

21. The molar ratio of Cl⁻, Br⁻, and I in a solution is 2:3:4. Now, if you want to pass Cl2 into the solution so that the molar ratio of Cl⁻, Br⁻, and I in the solution becomes 4:3:2, what is the molar ratio of Cl2 to be added and I in the original solution? (A) 1:2 (B) 1:3 (C) 1:4 (D) 1:5 (E) 1:6