Which equation represents the first electron affinity of chlorine?

a. cl (g) + e - → cl - (g)

b. 1 2 cl2 (g) + e - → cl - (g)

c. cl + (g) + e - → cl (g)

d. cl (g) → cl + (g) + e-?

Option-A [ Cl (g) + e ⁻ → Cl ⁻ (g) ] is the correct answer.

Explanation:

First electron affinity is the amount of heat evolved when an electron is added to a neutral atom.

Such problems often come in questions related to Born-Haber Cycle topic. Let suppose Mg and Cl ₂ is reacted to form MgCl ₂ crystal.

Then the Cl₂ gas is first atomized as follow,

Cl₂ → 2 Cl

After atomization an electron is added to neutral chlorine atoms, as,

Cl + e⁻ → Cl⁻

So, option A is correct choice.