Why is $N_2$ chemically inert?

$Sn$ is dissolved in excess of $NaOH$ solution,the compound obtained is

Phosphorus pentoxide $(P_4O_{10})$ is used as a ........ .

Write a balanced chemical equation for the reaction showing catalytic oxidation of $NH_3$ by atmospheric oxygen.

Consider the reaction:
$P_4 + 3 NaOH + 3 H_2 O \rightarrow Q + 3 NaH_2 PO_2$
Identify the reaction in which $Q$ is not the product. (Equations are not balanced)

The oxide which contains an odd electron at the nitrogen atom is ..... .