The question says “In the chemical reactions given above A and B respectively are”, but the actual reaction scheme is missing from the prompt.

So, the compounds $A$ and $B$ cannot be derived uniquely from first principles unless we know the reactions referred to by “given above”.

However, we can still analyze the options chemically.

1. Identify the roles of the given reagents

The recurring substances in the options are:

• $H_3PO_2$ = hypophosphorous acid
• $CH_3CH_2Cl$ = ethyl chloride
• $CH_3CH_2OH$ = ethanol

A very standard use of $H_3PO_2$ in organic chemistry is:

That is, it reduces a diazonium salt to the corresponding hydrocarbon.

Also, ethanol and ethyl chloride commonly appear in diazotisation / substitution-based conversion chains, but without the actual reaction sequence, we cannot prove which one is $A$ and which one is $B$.

2. Compare with the stored answer

The stored correct answer is A:

This is chemically plausible in standard nitrogen-compound conversion problems, where:

• one step uses $H_3PO_2$ to replace a diazonium group by hydrogen,
• another step may involve formation/use of ethyl chloride.

3. Final conclusion

Because the reaction scheme is absent, the answer cannot be independently derived with certainty from the prompt alone. But based on the provided stored answer and the common chemistry of $H_3PO_2$, the most plausible option is:

Option A.