21. Which of the following processes is expected to be exothermic? (A) Na+(g) + Br-(g) → NaBr(s) (B) Mg(g) → Mg2+(g) + 2 e- (C) MgCl2(s) → Mg(s) + Cl2(g) (D) O(g) + 2 e- → O2-(g) (E) KF(s) → K+(g) + F-(g)

10. Polystyrene is an addition polymer of styrene. What would be the effect if some divinylbenzene were added to styrene and then polymerized? (A) The second polymer would be made less flammable than pure polystyrene. (B) The polymer would be more flexible. Divinylbenzene acts as a plasticizer. (C) Divinylbenzene would act as a cross-linking agent, making the polymer stronger. (D) There would be no effect on the properties of the polymer. (E) There would be an effect, but it cannot be predicted.

21. Which of the following processes is expected to be exothermic?
(A) Na⁺(g) + Br^-(g) → NaBr(s)
(B) Mg(g) → Mg²⁺(g) + 2 e^-
(C) MgCl₂(s) → Mg(s) + Cl₂(g)
(D) O(g) + 2 e^- → O^2-(g)
(E) KF(s) → K⁺(g) + F^-(g)

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