Which element among the following forms $P \pi-P \pi$ multiple bonds?

The total number of paramagnetic gaseous products formed in all the following reactions $[A + B + C ]$:
$(A)\ NH_4 NO_3 \xrightarrow{\Delta} \text{Products}$
$(B)\ 3 NaNO_2 + 3 H_2 SO_4 \longrightarrow \text{Products}$
$(C)\ Pb(NO_3)_2 \xrightarrow{673 \ K} \text{Products}$

The reaction of $PCl_3$ with water produces ..........

Assertion : Although $PF_5, PCl_5$ and $PBr_5$ are known,the pentahalides of nitrogen have not been observed.
Reason : Phosphorus has lower electronegativity than nitrogen.

The correct decreasing order of basicity of hydrides of group-$15$ elements is

Which gas is used to provide an inert atmosphere?