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In which of the following pairs, electron gain enthalpies of constituent elements are nearly the same or identical? (a) Rb and Cs (b) Na and K (c) Ar and Kr (d) I and At Choose the correct answer from the options given below: (A) (a) and (b) only (B) (b) and (c) only (C) (a) and (c) only (D) (c) and (d) only

1. (A) (a) and (b) only
2. (B) (b) and (c) only
3. (C) (a) and (c) only
4. (D) (c) and (d) only

Correct answer: (B) (b) and (c) only

Solution

The electron gain enthalpies of Na and K, as well as Ar and Kr, are similar due to their positions in the periodic table, where elements in the same group exhibit comparable properties. In contrast, Rb and Cs, while also in the same group, have larger differences in their electron gain enthalpies due to their increased atomic size and shielding effects.

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