On reaction of $Lead$ $Sulphide$ with dilute nitric acid,which of the following is not formed?

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

Heating of ammonium dichromate produces

Nitrogen forms $NCl_3$ whereas phosphorus forms both $PCl_3$ and $PCl_5$. Why?

The total number of compounds having at least one bridging oxo group among the molecules given below is. . . . . . .
$N_2O_3, N_2O_5, P_4O_6, P_4O_7, H_4P_2O_5, H_5P_3O_{10}, H_2S_2O_3, H_2S_2O_5$

$PbF_4$ and $PbCl_4$ exist,while $PbBr_4$ and $PbI_4$ do not exist. This is due to: