Regarding the molecular orbital (MO) energy levels for homonuclear...

(i) $\mathrm{Ne}_2 \Rightarrow\left(\sigma 1 \mathrm{~s}^2\right)\left(\sigma^* 1 \mathrm{~s}^2\right)\left(\sigma 2 \mathrm{~s}^2\right)\left(\sigma^* 2 \mathrm{~s}^2\right)\left(\sigma 2 \mathrm{p}_{\mathrm{z}}^2\right)$\left(\pi 2 \mathrm{p}_{\mathrm{x}}^2=\pi 2 \mathrm{p}_{\mathrm{y}}^2\right)\left(\pi^* 2 \mathrm{p}_{\mathrm{x}}^2=\pi^* 2 \mathrm{p}_{\mathrm{y}}^2\right)\left(\sigma^* 2 \mathrm{p}_{\mathrm{z}}^2\right)$B.O.$=\frac{6-6}{2}=0$(ii)$\mathrm{F}_2 \Rightarrow\left(\sigma 1 \mathrm{~s}^2\right)\left(\sigma^* 1 \mathrm{~s}^2\right)\left(\sigma 2 \mathrm{~s}^2\right)\left(\sigma^* 2 \mathrm{~s}^2\right)$\left(\sigma 2 \mathrm{p}_{\mathrm{z}}^2\right)\left(\pi 2 \mathrm{p}_{\mathrm{x}}^2=\pi 2 \mathrm{p}_{\mathrm{y}}^2\right)\left(\pi^* 2 \mathrm{p}_{\mathrm{x}}^2=\pi^* 2 \mathrm{p}_{\mathrm{y}}^2\right)$ (iii) $\mathrm{O}_2^{\oplus} \Rightarrow\left(\sigma 1 s^2\right)\left(\sigma^* 1 s^2\right)\left(\sigma 2 s^2\right)\left(\sigma^* 2 s^2\right)\left(\sigma 2 p_z^2\right)\left(\pi 2 p_x^2=\pi 2 p_y^2\right)\left(\pi^* 2 p_x^1=\pi^* 2 p_y\right)$ B.O. $=\frac{6-1}{2}=2.5$ $\mathrm{O}_2 \Rightarrow\left(\sigma 1 s^2\right)\left(\sigma^* 1 s^2\right)\left(\sigma 2 s^2\right)\left(\sigma^* 2 s^2\right)\left(\sigma 2 p_{\mathrm{z}}^2\right)\left(\pi 2 p_{\mathrm{x}}^2=\pi 2 p_{\mathrm{y}}^2\right)\left(\pi^* 2 p_{\mathrm{x}}^1=\pi^* 2 p_{\mathrm{y}}^1\right)$ B.O. $\frac{6-2}{2}=2$ (Bond order increases, Bond strength increases) (iv) Size of atom increases, Bond length increases Size of Li > B So, Bond length of $\mathrm{Li}_2>\mathrm{B}_2$