Which of the following combines with $Fe(II)$ ions to form a brown complex?

The bond energies (in $kJ \ mol^{-1}$) of $P-H$, $As-H$, and $N-H$ are respectively:

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

The number of $H$ atoms attached to the phosphorus atom in hypophosphorous acid is

Find the element, which displays greater ability to form $p \pi-p \pi$ multiple bonds to itself and to other elements in the same block.

Which of the following elements does not exhibit the inert pair effect?