Question

Identify the least stable ion amongst the following :

• A. $L{i}^{-}$
• B. $B{e}^{-}$
• C. $B^{-}$
• D. $C^{-}$

Answer 1

The correct option is B $B{e}^{-}$

$L{i}^{-}:1s^2,2s^2;B{e}^{-}:1s^2,2s^2,2p^1.$ In $Li$, addition of electron has taken place in 2s orbital; in $B{e}^{-}$, addition of electron has taken place in 2p orbital loosing its 2s completely filled configuration.

$E{A}_1$ for $Be$ is more positive than $E{A}_1$ for $Li$.

Thus, $B{e}^{-}$ is the least stable.