Compounds of nitrogen and phosphorus is/are correct?

Option A: $\mathrm{(NH_4)_2Cr_2O_7\xrightarrow{\Delta}N_2+Cr_2O_3+4H_2O}$ (the volcano reaction), and $\mathrm{NH_4NO_3\xrightarrow{\sim520\,K}N_2O+2H_2O}$, so both parts are correct. Option B: $\mathrm{N_2O_3}$ reacts with water to give nitrous acid, $\mathrm{HNO_2}$, with nitrogen in the $+3$ state, so it is the anhydride of $\mathrm{HNO_2}$, while $\mathrm{N_2O_5}$ is the anhydride of $\mathrm{HNO_3}$; B is wrong. Option C: $\mathrm{H_3PO_3}$ is $\mathrm{HPO(OH)_2}$, with one $\mathrm{P{-}H}$ bond and two ionisable $\mathrm{O{-}H}$ groups, so it is dibasic, not tribasic, and C is wrong. Option D: with excess ammonia, chlorine gives $\mathrm{N_2}$ and $\mathrm{NH_4Cl}$, but with excess chlorine the product is explosive $\mathrm{NCl_3}$, so D is wrong. Only A is correct.