Electron gain enthalpy is greater than zero for

Options

A. `Na`
B. `Mg`
C. `A1`
D. `Sn`

Answer

B

Explanation

The outermost shell electron configuration of the alkaline earth metals is `ns^(@)`. For the process
`M(g) +e^(-)rarr M^(-)(g)`
where `M` denotes a member of group `2` family, the extra electron must enter the `np` subshell, which is effectively shielded by the two `ns` electron (the `np` electrons are farther away from the nucleus than the `ns` eletrons) and the inner electrons. consequently, alkaline earth metals such as `Mg` have no natural tendecy to pick up an extra electrons as they from unstable anions. An atom that forms an ustable anion on addition of an eletron has a positive value of `Delta_(eg)H`.