MCQ
Identify the least stable ion amongst the following :
- A$\ce{Li}^-$
- B$\ce{Be}^-$
- ✓$\ce{B}^-$
- D$\ce{C}^-$
✓
Answer
Correct option: C.
$\ce{B}^-$
The configuration of $\ce{Li}$ is $\ce{1s^22s^1}$. Adding one $\ce{e}^-$ will fill its $2s$ subshell providing it extra stability.
The configuration of $\ce{Be}$ is $\ce{1s^22s^2}$. Adding one $\ce{e}^-$ will disturb its stable fully filled configuration. So, it is the least stable among all.
The configuration of $B$ is $\ce{1s^22s^22p^1}$. 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 $\ce{1s^22s^22p^2}$. It does not have half $-$ filled or fully filled configuration so adding one $e^-$ its configuration becoes $\ce{1s^22s^22p}^3$ that it is a half $-$ filled configuration and becomes stable.
The configuration of $\ce{Be}$ is $\ce{1s^22s^2}$. Adding one $\ce{e}^-$ will disturb its stable fully filled configuration. So, it is the least stable among all.
The configuration of $B$ is $\ce{1s^22s^22p^1}$. 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 $\ce{1s^22s^22p^2}$. It does not have half $-$ filled or fully filled configuration so adding one $e^-$ its configuration becoes $\ce{1s^22s^22p}^3$ that it is a half $-$ filled configuration and becomes stable.
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