Question

The formation of the oxide ion O2–(g) requires first an exothermic and then an endothermic step as shown below :

O(g) + e– = O–(g) ; $\Delta$H⁰ = – 142 kJmol–1

O– (g) + e– = O2– (g) ; $\Delta$H⁰ = 844 kJmol–1

This is because :

• A. Oxygen is more electronegative.
• B. Oxygen has high electron affinity.
• C. O– ion will tend to resist the addition of another electron.
• D. O– ion has comparatively larger size than oxygen atom.

Answer 1

Answer: (C)

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

Answer 2

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