When concentrated nitric acid is heated,it decomposes to give

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$ : $PH_3$ has lower boiling point than $NH_3$.
Reason $(R)$ : In liquid state $NH_3$ molecules are associated through van der Waals forces,but $PH_3$ molecules are associated through hydrogen bonding.
In the light of the above statements,choose the most appropriate answer from the options given below:

What happens when nitrogen dioxide $(NO_2)$ dissolves in water?

Which of the following elements forms oxides in all oxidation states from $+I$ to $+V$?

Nitrogen can be obtained from air by removing

The strongest base is