The reagent used for the Gatterman-Koch formylation of arene is

Identify the major product $X$ formed in the following reaction:

$CH_3-COOH \xrightarrow[\Delta]{Ca(OH)_2} (A)$
Product $(A)$ is

$C_6H_5CH_3$ $\xrightarrow{CrO_2Cl_2} A$ $\xrightarrow{H_2O} B$
The functional group present in $B$ and the name of the reaction are:

$A, B$ and $C$ respectively are

In the reaction $\underset{\text{(Vapour)}}{C_2H_5OH} \xrightarrow[300^{\circ}C]{Cu} X$. The molecular formula of $X$ is