31.A protein mixture contains three proteins with molecular weights of 15 kDa, 50 kDa, and 120 kDa. You need to separate them effectively based on molecular weight for downstream analysis. Which chromatographic technique would be the most appropriate?
(A) Ion exchange chromatography.
(B) Size-exclusion chromatography.
(C) Affinity chromatography.
(D) Gas chromatography.
(E) Reverse-phase chromatography.

1.Which equation correctly describes the change in Gibbs free energy for a reaction at non-standard conditions? (A) AG = AG° + RT ln(Q) (B) AG = ΔΗ - TAS (C) AG = -RT ln(K) (D) AG = RT In(Q/K) (E) AG = AG° - RT ln(K)

2.In a system at equilibrium, how are AG and the equilibrium constant K related? (A) AG = 0; K = 1 (B) AG° = -RT ln(Q/K) (C) AG ＞ 0; K ＜ 1 (D) AG = RT ln(K) (E) AG° = -RT ln(K)

3.What is the primary effect of adding a catalyst to a reversible reaction at equilibrium? (A) Increases the forward rate only. (B) Shifts the equilibrium constant. (C) Alters the reaction enthalpy. (D) Increases the activation energy required for the reaction. (E) Increases the rates of both forward and reverse reactions equally.

4.Who did not contribute the Atomic Theory? (A) John Dalton (B) Emil Fischer (C) Ernest Rutherford (D) James Chadwick (E) J. J. Thomson

5.Indicate which of the following sets of quantum numbers (n, l, ) in an atom is acceptable: (A) (1, 0, 2, -1/2) (B)(C)(D)(E) (3, 2, 1, 1)

6.Phenyl Grignard reagent reacts with 2-methylpropanal to form a secondary alcohol. The ＜sup＞1＜/sup＞H NMR spectrum of 2-methylpropanal displays the two methyl groups as equivalent (a single doublet at δ 1.1). However, in the product alcohol (a racemic mixture), the ＜sup＞1＜/sup＞H NMR now shows two distinct 3H doublets, one at δ 0.75 and one around δ 1.0. Why do the two methyl groups in the product have different NMR chemical shifts? What is the term applied to such protons? (A) The presence of the hydroxyl group creates an asymmetric center, making the methyl groups homotopic. (B) The formation of a chiral center in the product makes the two methyl groups diastereotopic, meaning they experience different chemical environments. (C) The hydroxyl group participates in hydrogen bonding, causing different splitting patterns for the methyl groups, which are now homotopic. (D) The two methyl groups in the product remain chemically equivalent, and the observed difference in NMR chemical shifts is due to rotational averaging. (E) The steric hindrance of the bulky phenyl group shields one methyl group, making them enantiotopic rather than diastereotopic.

7.What does the pre-exponential factor in the Arrhenius equation represent? (A) Activation energy. (B) Reaction probability. (C) Temperature dependence. (D) Molecular orientation during collisions. (E) Frequency of collisions.

8.How does enzyme turnover number (k＜sub＞cat＜/sub＞) relate to reaction velocity? (A) Determines the maximum reaction velocity when the enzyme is saturated with substrate. (B) Reflects the enzyme's catalytic efficiency relative to substrate concentration. (C) Is directly proportional to the rate constant for enzyme-substrate binding. (D) Indicates the fraction of substrate molecules converted to product per second. (E) Describes the maximum catalytic rate normalized by the enzyme’s molecular weight.

9.A researcher is studying an enzyme-catalyzed reaction and observes that adding a certain compound decreases the reaction rate without affecting the substrate binding at the active site. Which mechanism most likely explains this observation? (A) The compound increases substrate affinity. (B) The compound stabilizes the enzyme’s active form. (C) The compound induces a conformational change, reducing enzyme activity. (D) The compound decreases the reaction rate by irreversibly inhibiting the enzyme. (E) The compound physically blocks the active site, preventing substrate binding.

10.The following NMR spectrum corresponds to a compound with the molecular formula . Propose a structure and explain how it is consistent with the observed absorptions. (A)Ⅰ (B)Ⅱ(C)Ⅲ(D)Ⅳ(E)Ⅴ

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