When $LiN{O}_3$ is heated, it gives oxide, $L{i}_{2}O$, whereas other alkali metal nitrates decompose to give corresponding :

The correct option is A nitrite
Due to the small size of $L{i}^{+}$, it is very polarizing and favours the formation of $Li{O}_2$.

$4Li{O}_3\to 2L{i}_{2}O+4N{O}_2+O_2$

While other alkali metal nitrates decomposes to give corresponding nitrite.

$NaN{O}_3\stackrel{\Delta }{\to }NaN{O}_2+\frac{1}{2}{O}_2$