(b) \(\mathrm{Li}_{2}-<\mathrm{Li}_{2}^{+}<\mathrm{Li}_{2}\)

Explanation:

\(\mathrm{Li}_{2}(3+3=6)=\sigma 1 \mathrm{s}^{2}, \quad \hat{\sigma} 1 \mathrm{s}^{2}, \sigma 2 \mathrm{s}^{2}\)

Bond order \(=\frac{N_{b}-N_{a}}{2}=\frac{4-2}{2}=1\)

\(\mathrm{Li}_{2}^{+}(3+3-1=5)=\sigma 1 \mathrm{s}^{2}, \dot{\sigma}^{2} 1 s^{2}, \cdot \sigma 2 s^{1}\)

Bond order \(=\frac{3-2}{2}=\frac{1}{2}=0.5\)

Bond order \(=\frac{4-3}{2}=\frac{1}{2}=0.5\)

Stability order is \(\mathrm{Li}_{2}>\mathrm{Li}_{2}^{+}>\mathrm{Li}_{2}^{-}\) (because Li \(_{2}^{-}\) have more number of electrons in antibonding orbitals which destabilises the species).