In the presence of dil. $HCl$,compound $A$ is converted to a constitutional isomer $(B)$. Compound $B$ is:

The intermediate $J$ in the following Wittig reaction is

Keto-enol tautomerism is observed in which of the following?

Which of the following reagents must be used in the given interconversion? The reaction involves the reduction of $4$-hydroxycyclohexanone to cyclohexanol,where the carbonyl group is reduced to a methylene group while the hydroxyl group remains unaffected.

Complete each synthesis by providing the missing starting material, reagent, or products for the following reactions:

Consider the reaction sequence and identify $'C'$.
$A + B \xrightarrow{dil \ NaOH / \Delta} C$
(The reaction sequence is: $3,3-\text{dimethylbut-1-ene} \xrightarrow[(ii) Zn/H_2O]{(i) O_3} A + B$)