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JEE Main · 2022 · 28 Jul 2022 · Shift 1 · Classification of Elements and Periodicity

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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:
  1. (A)(A) and (B) only
  2. (B)(B) and (C) only
  3. (C)(A) and (C) only✓ Correct
  4. (D)(C) and (D) only

Answer: (C)

Solution

Rb and Cs (both alkali metals in the same group) have nearly identical electron gain enthalpies (around -46 kJ/mol) due to similar electronic configurations. Ar and Kr (noble gases) both have positive electron gain enthalpies (around +96 kJ/mol) because adding an electron to a stable noble gas configuration is energetically unfavorable. Thus, pairs (A) and (C) have nearly the same electron gain enthalpies.

JEE Main · 2022 · 28 Jul 2022 · Shift 1 · Single correct option

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