Which one of the following elements occurs free in nature?

In the following reaction,identify the nature of the product formed by the complete hydrolysis of the underlined atom at $R.T.$:
$\underline{N}_2O_5 + H_2O \longrightarrow 2HNO_3$

When $PbO_2$ reacts with concentrated $HNO_3$,the evolved gas is:

Ammonia is liberated in the reaction of

$A + H_2O \to B + HCl$ and $B + 3H_2O \to C + 3HCl$. Compounds $(A)$,$(B)$,and $(C)$ are respectively:

Which of the following processes is used for the production of $HNO_3$ to obtain a good yield?