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.

9. In preparation for the combustion demonstration, the assistant instructor injected equal molar amount of H2 and O2 into the balloon, but the demonstration had to be postponed until the next day due to safety setup problems. During the night, both gases leaked through the pores of the balloon. What is the molar ratio of O2 to H2 in the balloon the next day if 30% of the H2 is leaking? (A) 0.76 (B) 0.95 (C) 1.14 (D) 1.32 (E) 1.60

10. The following statements describe the chemical and physical properties of some representative elements and their compounds. Which statement is   incorrect  ? (A) Diborane (B2H6) has two three-center two-electron B-H-B bonds. (B) Lithium metal is converted to lithium superoxide in the presence of excess molecular oxygen. (C) Al2O3 is amphoteric and can dissolve in both acidic and basic solutions. (D) The hydration of F¯ decreases the entropy when HF dissociates in water, which contributes to make HF a weaker acid than HCl and HBr. (E) SiC is an extremely hard substance because it has a covalent network structure similar to diamond.

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)

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

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.

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]