Q6 / 160 · TS EAMCET 2022 (19 Jul Shift 2) · Chemistry
Identify all the species that do not exist
$$
\mathrm{H}_2^{+}, \mathrm{He}_2^{2+}, \mathrm{Li}_2^{2-}, \mathrm{Ne}_2, \mathrm{Be}_2^{-}, \mathrm{He}_2
$$
- A$\mathrm{He}_2, \mathrm{Ne}_2$ only
- Correct answerB$\mathrm{Li}_2^{2-}, \mathrm{Ne}_2, \mathrm{He}_2$ only
- C$\mathrm{Be}_2^{-}, \mathrm{He}_2, \mathrm{Ne}_2$ only
- D$\mathrm{H}_2^{+}, \mathrm{Li}_2^{2-}$ only
Solution
Electronic configuration of
$$
\begin{aligned}
& \mathrm{Li}_2^{2-}=\sigma 1 \mathrm{~s}^2 \sigma^* 1 \mathrm{~s}^2 \sigma 2 \mathrm{~s}^2 \sigma^* 2 \mathrm{~s}^2 \\
& \Rightarrow \quad \text { B.O. }=0
\end{aligned}
$$
Electronic configuration of
$$
\begin{aligned}
& \mathrm{He}_2=\sigma 1 \mathrm{~s}^2 \sigma^* 1 \mathrm{~s}^2 \\
& \Rightarrow \text { B.O. }=0
\end{aligned}
$$
Electronic configuration of
$$
\begin{aligned}
& \mathrm{Ne}_2=\sigma 1 \mathrm{~s}^2 \sigma^* 1 \mathrm{~s}^2 \sigma 2 \mathrm{~s}^2 \sigma^* 2 \mathrm{~s}^2 \\
& \sigma 2 \mathrm{pz}^2 \pi 2 \mathrm{px}^2 \pi 2 \mathrm{py}^2 \pi^* 2 \mathrm{px}^2 \\
& \pi^* 2 \mathrm{py}^2 \sigma^* 2 \mathrm{pz}^2 \\
& \Rightarrow \quad \text { B.O. }=0
\end{aligned}
$$
Hence, $\mathrm{Li}_2^{2-}, \mathrm{Ne}_2$ and $\mathrm{He}_2$ does not exist.
Hence, the correct answer is option: 'B'.