The correct order of stability

$$\begin{gathered} {\mathrm{H}}_2: \mathrm{\sigma }1{\mathrm{s}}^2 ; \mathrm{B}.\mathrm{O}=\frac{2-0}{2}=1 \\ {\mathrm{H}}_2^{+}: \mathrm{\sigma }1{\mathrm{s}}^1 ; \mathrm{B}.\mathrm{O}=\frac{1}{2}=0.5 \\ {\mathrm{He}}_2 : \mathrm{\sigma }1{\mathrm{s}}^2\mathrm{\sigma }*1{\mathrm{s}}^2 ; \mathrm{B}.\mathrm{O}=\frac{2-2}{2}=0 \\ {\mathrm{He}}_2^{+} : \mathrm{\sigma }1{\mathrm{s}}^2\mathrm{\sigma }*1{\mathrm{s}}^1 ; \mathrm{B}.\mathrm{O}=\frac{1}{2}=0.5 \end{gathered}$$

As bond order increases, stability increases.

Bond order for both ${\mathrm{H}}_2^{+} \mathrm{and} {\mathrm{He}}_2^{+}$​ is same but ${\mathrm{H}}_2^{+}$ is more stable than ${\mathrm{He}}_2^{+}$​ due to absence of electrons in anti-bonding orbital.

Hence, ${\mathrm{H}}_2>{\mathrm{H}}_2^{+}>{\mathrm{He}}_2^{+}>{\mathrm{He}}_2$.