Lithium forms $L{i}_{2}O$ while other alkali metals form peroxides and super oxides because:

The correct option is C the smaller $L{i}^{+}$ ion cannot stabilize the larger peroxide or super oxide ion
The lithium ion is small in size. it cannot stablize larger peroxide or superoxide ion. Thus when burnt in air, lithium forms the monoxide and others form peroxides or superoxides.