Question

The least stable ion in the following is:

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

Answer 1

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

$Be:1s^{2}2s^2$
$2s$ orbital is completely filled. On adding one more electron, it will go in $2p$, which makes $B{e}^{-}$unstable.