Why is nitrogen chemically inert?

Which of the following oxides is the anhydride of orthophosphoric acid?

Identify the correct orders from the following with respect to the property associated with:
$A$. $NH_3 > PH_3 > AsH_3 > SbH_3$ - Bond Angle
$B$. $NH_3 > PH_3 > AsH_3 > SbH_3$ - Basic Character
$C$. $PH_3 > AsH_3 > SbH_3 > NH_3$ - Thermal stability
$D$. $SbH_3 > NH_3 > AsH_3 > PH_3$ - Boiling point

Which of the following oxides of nitrogen is paramagnetic?

Which of the following oxides of nitrogen is a coloured gas?

Among the following,cyclic species are :
$I$. $H_5P_3O_{10}$ $II$. $[B_3O_3(OH)_5]^{2-}$ $III$. $H_5P_5O_{15}$ $IV$. $P_3N_3Cl_6$