Which gas gives white fumes with $HCl$?

Pentavalency in phosphorus is more stable when compared to that of nitrogen,even though they belong to the same group. This is due to:

When $KNO_3$ is heated with concentrated $H_2SO_4$,brown fumes are evolved. These fumes are due to:

Assertion $(A)$: In group $15$ elements, nitrogen does not form pentahalides.
Reason $(R)$: Nitrogen can exhibit $+5$ oxidation state.
The correct option among the following is:

Which of the following elements forms $p\pi-p\pi$ bond with itself?

Which is the correct sequence in the following properties? For the correct order mark $(T)$ and for the incorrect order mark $(F)$.
$(a)$ Lewis acidity order : $SiF_4 < SiCl_4 < SiBr_4 < SiI_4$
$(b)$ Melting point : $NH_3 > SbH_3 > AsH_3 > PH_3$
$(c)$ Boiling point : $NH_3 > SbH_3 > AsH_3 > PH_3$
$(d)$ Dipole moment order : $NH_3 > SbH_3 > AsH_3 > PH_3$