Caesium forms a stable superoxide $\mathrm{CsO}{}_2$ in excess oxygen, whereas lithium gives only $\mathrm{Li}{}_2\mathrm{O}$ and $\mathrm{LiO}{}_2$ is not obtained under normal conditions. The best explanation is:

1. Acaesium has a higher first ionisation enthalpy than lithium and so oxidises oxygen further
2. Bthe $\mathrm{O}{}_2{}^{-}$ ion is smaller than $\mathrm{O}{}^{2-}$ and so fits better around $\mathrm{Li}{}^{+}$
3. Ca large cation is best able to stabilise the large $\mathrm{O}{}_2{}^{-}$ ion in the crystal, while the small, strongly polarising $\mathrm{Li}{}^{+}$ favours the small $\mathrm{O}{}^{2-}$ with its much higher lattice energy
4. Dlithium is not electropositive enough to transfer an electron to oxygen