The number of $P-OH$ bonds and the oxidation state of the phosphorus atom in pyrophosphoric acid $(H_4P_2O_7)$ respectively are

The laughing gas is

Zinc on reaction with concentrated nitric acid gives an oxide of nitrogen $(A)$. Zinc with dilute nitric acid gives another oxide of nitrogen $(B)$. Oxidation numbers of nitrogen in $(A)$ and $(B)$ are respectively:

Nitrogen is obtained when $NaNO_2$ reacts with

How can you synthesise nitric oxide in the laboratory?

Choose the correct statement$(s)$ among the following.
$A$. $SnCl_2 \cdot 2 H_2O$ is a reducing agent.
$B$. $SnO_2$ reacts with $KOH$ to form $K_2[Sn(OH)_6]$.
$C$. $A$ solution of $PbCl_2$ in $HCl$ contains $Pb^{2+}$ and $Cl^{-}$ ions.
$D$. The reaction of $Pb_3O_4$ with hot dilute nitric acid to give $PbO_2$ is a redox reaction.