An organic compound A on reaction with thionyl chloride, gives compound B. Compound B, reacts with sodium in dry ether as solvent, gives 2,3-dimethyl butane. Identify compound A.

Compound B reacts with sodium in dry ether to give 2,3-dimethylbutane. This is a Wurtz reaction.

$2R-Cl + 2Na \xrightarrow{\text{dry ether}} R-R + 2NaCl$

Since the product $R-R$ is 2,3-dimethylbutane, $(CH_3)_2CH-CH(CH_3)_2$, the alkyl group $R$ must be an isopropyl group, $(CH_3)_2CH-$.

Therefore, compound B is isopropyl chloride, $(CH_3)_2CH-Cl$.

Compound A reacts with thionyl chloride ($SOCl_2$) to give compound B. This indicates that compound A is an alcohol.

$R-OH + SOCl_2 \rightarrow R-Cl + SO_2 + HCl$

Thus, compound A is isopropyl alcohol, $(CH_3)_2CH-OH$.

Answer: Isopropyl alcohol