Phosphorus forms a number of oxyacids. Out of these oxyacids, phosphinic acid has strong reducing property. Write the structure of acid and also write a reaction showing its reducing behaviour.

$\left(\mathrm{i}\right)$ An inorganic iodide $\left(\mathrm{A}\right)$ on heating with a solution of $\mathrm{KOH}$ gives a gas $\left(\mathrm{B}\right)$ and the solution of compound $\left(\mathrm{C}\right)$.

$\left(\mathrm{ii}\right)$ The gas $\left(\mathrm{B}\right)$ on ignition in air gives a compound $\left(\mathrm{D}\right)$ and water.

$\left(\mathrm{iii}\right)$ Copper sulphate is finally reduced to the metal on passing $\left(\mathrm{B}\right)$ through its solution.

$\left(\mathrm{iv}\right)$ Precipitate of compound $\left(\mathrm{E}\right)$ is formed on reaction of $\left(\mathrm{C}\right)$ with copper sulphate solution.

Identify $\left(\mathrm{A}\right)$ to $\left(\mathrm{E}\right)$ and give chemical equations for steps $\left(\mathrm{i}\right)$ to $\left(\mathrm{iv}\right)$.

The gas (B) is a group 15 hydride which is colourless with rotten fish smell and is highly poisonous. The gas $\left(\mathrm{B}\right)$ on ignition in air gives a compound $\left(\mathrm{D}\right)$ and water.

Identify the compound D and the gas B in the above reaction.

An inorganic iodide (A) on heating with a solution of KOH gives a gas (B) and the solution of compound (C). Precipitate of compound $\left(\mathrm{E}\right)$ is formed on reaction of $\left(\mathrm{C}\right)$ with copper sulphate solution Identify the compound (E) and give chemical equations.