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]

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

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

22. Methane monooxygenase (s-MMO) contains a dinuclear iron active center and is a catalyst for the oxidation of CH4 by O2 to form CH3OH; the reaction process is shown below. Which of the following statements is incorrect? (A) Theelectronic configuration of the ground state Fe atom is [Ar]3d64s². involves the breaking of a non-polar bond and the formation of (B) Step polar bonds. (C) Electron transfer occurs between iron and oxygen atoms in each step. (D) Radical species are produced during the reaction. (E) The overall reaction shown is CH4 + O2 + 2H⁺ +2 CH3OH+ H2O

23. Which pair of the following compounds that measured under the same conditions have the same amplitude of specific rotation but with opposite direction? (A) cis-1,2-dichlorocyclopentane and trans-1,2-dichlorocyclopentane (B) (2S, 3R)-butane-2,3-diol and (2R, 3S)-butane-2,3-diol (C) cis-2-butene and trans-2-butene (D) (2S, 3R)-butane-2,3-diol and (2R, 3R)-butane-2,3-diol (E) D-glucose and L-glucose

24. (i) The number of the following species which exhibit resonance is a. O3, SeO2, NF3, N2O, CCl4, SCN⁻, OF2 (ii) The number of the following diatomic species which are paramagnetic is b.  What is (a + b)? (A) 5 (B) 6 (C) 7 (D) 8 (E) 9

25. 2-Methoxy-2-methylbutane (TAME) is commonly used as a gasoline additive. With the presence of appropriate catalysts, TAME can be produced by the liquid- liquid reaction between methanol and olefins, in which the following reactions occur simultaneously. The equilibrium constants Kx, expressed in terms of the amount fraction of the substance, for reactions I, II, and III are shown above. What is the range of values of ?  (A) ＜-1 (B)-1~0 (C) 0~1 (D) ＞ 1  (E)