Question

In a period, from the left to right the electron affinity increases, but alkaline earth metals have lower electron affinity than alkali metals because______

• A. Alkaline earth metals have lesser atomic radius than alkali metals.
• B. Alkaline earth have higher electronegativity than alkali metals.
• C. Alkaline earth metals have completely filled 's' orbitals.
• D. Alkaline earth metals have lesser electronegativity than alkali metals.

Answer 1

The correct option is C Alkaline earth metals have completely filled 's' orbitals.

Alkali metals have a valence electron configuration of $n{s}^1$ so they can accept another electron in the ns orbital.

On the other hand, alkaline earth metals have a valence electron configuration of $n{s}^2$.

Alkaline earth metals have little tendency to accept another electron, as it would have to go into a higher energy p orbital.

Option C is correct.