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# Stability of the species $Li_2,Li_2^-$ and $Li_2^+$ increases in the order

$\begin{array}{1 1}(a)\;Li_2^- < Li_2 < Li_2^+\\(b)\; Li_2 < Li_2^+ < Li_2\\(c)\;Li_2^- < Li_2^+ < Li_2\\(d)\;Li_2 < Li_2^- < Li_2^+\end{array}$

$Li_2(6):\sigma _{1s}^2\sigma_{1s}^*{^2}\sigma _{2s}^2$
Bond order of $Li_2=\large\frac{4-2}{2}\Rightarrow \large\frac{2}{2}$$=1 Bond order of Li_2^+=\large\frac{4-1}{2}$$\Rightarrow 1.5$
Bond order of $Li_2^-=\large\frac{4-3}{2}$$\Rightarrow 0.5$
Stability $\propto$ Bond order
$\therefore$Stability :$Li_2^- < Li_2 < Li_2^+$
Hence (a) is the correct answer.