Which of the following is an oxoacid?

The decrease in stability of the higher oxidation state in the $p-$block elements with an increasing atomic number is due to:

An inorganic salt $(A)$ is decomposed at about $523 \ K$ to give products $(B)$ and $(C).$ Compound $(C)$ is a liquid at room temperature and is neutral to litmus paper,while oxide $(B)$ on burning with white phosphorus,gives a dehydrating agent $(D).$ Compounds $(A)$,$(B)$,$(C)$ and $(D)$ will be identified as:

White phosphorus reacts with thionyl chloride to form $PCl_3$ along with $A$ and $B$. $A$ and $B$ respectively are

Inertness of $N_2$ gas is due to

$HNO_3$ is produced in good yield by which of the following methods?