On heating, LiNO$$_3$$ gives how many compounds among the following?
Li$$_2$$O, N$$_2$$, O$$_2$$, LiNO$$_2$$, NO$$_2$$

We need to determine how many compounds from the given list are produced when LiNO$$_3$$ is heated.

Thermal decomposition of LiNO$$_3$$.

Lithium nitrate behaves differently from other alkali metal nitrates upon heating. Unlike NaNO$$_3$$, KNO$$_3$$, etc., which decompose to give the corresponding nitrite and O$$_2$$, lithium nitrate decomposes similar to alkaline earth metal nitrates due to the small size and high polarizing power of Li$$^+$$.

Write the decomposition reaction.

$$4\text{LiNO}_3 \xrightarrow{\Delta} 2\text{Li}_2\text{O} + 4\text{NO}_2 + \text{O}_2$$

Identify the products from the given list.

The products are:

Li$$_2$$O — Yes, it is a product.

N$$_2$$ — No, nitrogen gas is not produced.

O$$_2$$ — Yes, it is a product.

LiNO$$_2$$ — No, lithium nitrite is not formed (unlike other alkali metal nitrates).

NO$$_2$$ — Yes, it is a product.

Three compounds from the list are produced: Li$$_2$$O, O$$_2$$, and NO$$_2$$.

The correct answer is 3.