Basicity of phosphinic acid is

Cyanogen gas is obtained in the reaction:

The stable bivalency of $Pb$ and trivalency of $Bi$ is

The mixture of $B$ and $C$ are :
$NO \xrightarrow{O_2} A \rightleftharpoons D$
$A \xrightarrow{NaOH \ (aq.)} [B + C]$

Phosphine is generally prepared in the laboratory by:

Match the following List-$I$ (Acid) with List-$II$ (Reagents used for preparation):
| List-$I$ (Acid) | List-$II$ (Reagents used for preparation) |
| :--- | :--- |
| $A. H_3PO_2$ | $I. \text{Red } P_4 \text{alkali}$ |
| $B. H_4P_2O_5$ | $II. \text{White } P_4 \text{alkali}$ |
| $C. H_3PO_4$ | $III. PCl_3; H_3PO_3$ |
| $D. H_4P_2O_7$ | $IV. P_2O_5; H_2O$ |
| | $V. H_3PO_4; \Delta$ |