The least stable in amongst the following is :

Options

A. `C^(-)`
B. `Li^(-)`
C. `B^(-)`
D. `Be^(-)`

Answer

D

Explanation

`Li(1s^(2)2s^(1))rarr Li^(-)(1s^(2)2s^(2))`
`Be(1s^(2)2s^(2))rarr Be^(-)(1s^(2)2s^(2)2p^(1))`
`B(1s^(2)2s^(2)2p^(1))rarr B^(-) (1s^(2)2s^(2)2p^(2))` ltbrltgt `C(1s^(2)2s^(2)2p^(2)) rarr C^(-)(1s^(2)2s^(2)2p^(3))`
`Be^(-)` is the least stable because `Be` has relatively stable configuration in the from of completely full subshell. this is destabilized when an electron in added to it.