The formation of the oxide ion O 2– (g) requires first an e…

Chemistry Classification of Elements and Periodicity JEE ADVANCED Previous Year Question Single Correct MCQ

Published by: CGP EDU Academic Team

Published on: August 14, 2026

The formation of the oxide ion O 2– (g) requires first an exothermic and then an endothermic step as shown below:

O (g) + e – = O – (g) ; Δ H° = – 142 kJmol –1 O

– (g) + e – = O 2– (g) ; Δ H° = 844 kJmol –1

This is because:

oxygen is more electronegative.

oxygen has high electron affinity.

O – ion will tend to resist the addition of another electron.

O – ion has comparatively larger size than oxygen atom.

Text Solution

Verified by Experts

The correct answer is:

The addition of second electron in an atom or ion is always endothermic because of repulsion between two negative charges.

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