MCQ
The least stable ion is
- A$Li^-$
- ✓$Be^-$
- C$B^-$
- D$C^-$
✓
Answer
Correct option: B.
$Be^-$
b
The configuration of $Li$ is $1 s ^2 \,2 s ^1$. Adding one $e ^{-}$will fill its $2 s$ subshell providing it extra stability.
The configuration of $Li$ is $1 s ^2 \,2 s ^1$. Adding one $e ^{-}$will fill its $2 s$ subshell providing it extra stability.
The configuration of $Be$ is $1 s ^2\, 2 s ^2$. Adding one $e ^{-}$will disturb its stable fully filled configuration. So, it is the least stable among all.
The configuration of $B$ is $1 s ^2 \,2 s ^2\, 2 p ^1$. It does not have half-filled or fully filled configuration so adding one $e ^{-}$will not disturb its stable configuration.
The configuration of $C$ is $1 s ^2 \,2 s ^2\, 2 p ^2$. It does not have half-filled or fully filled configuration so adding one $e ^{-}$its configuration becoes $1 s ^2\, 2 s ^2 \,2 p ^3$ that it is a half-filled configuration and becomes stable.
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