The number of hydrogen atom$(s)$ attached directly to the phosphorus atom in hypophosphorous acid $(H_3PO_2)$ is:

The number of bridged oxygen atoms present in compound $B$ formed from the following reactions is
$Pb(NO_3)_2 \xrightarrow{673 \ K} A + PbO + O_2$
$A \xrightarrow{\text{Dimerise}} B$

$(NH_4)_2Cr_2O_7$ on heating gives:

Identify the reactions in which $N_2$ is liberated.
$a. \ (NH_4)_2SO_4 + NaOH \longrightarrow$
$b. \ NH_3 + Cl_2 \longrightarrow$ (excess $Cl_2$ is not specified,but $N_2$ is formed when $NH_3$ is in excess)
$c. \ (NH_4)_2Cr_2O_7 \xrightarrow{\Delta}$
$d. \ NH_4NO_3 \xrightarrow{\Delta}$
$e. \ NH_4Cl_{(aq)} + NaNO_{2_{(aq)}} \longrightarrow$

$PCl_3$ reacts with water to form:

Select the compound in which $HCl$ is not the product of hydrolysis.