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

Question

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