In the reaction:
$C_6H_5-H \xrightarrow{[X] / AlCl_3} C_6H_5-C(=O)-CH_2-C_6H_5$
$[X]$ will be:

Write the structures of products of the following reactions:
$(i)$ Benzene + $C_{2}H_{5}COCl$ $\xrightarrow{\text{Anhyd. } AlCl_{3}, CS_{2}}$
$(ii)$ $(C_{6}H_{5}CH_{2})_{2}Cd + 2 CH_{3}COCl \rightarrow$
$(iii)$ $H_{3}C - C \equiv C - H$ $\xrightarrow{Hg^{2+}, H_{2}SO_{4}}$
$(iv)$ $p$-Nitrotoluene $\xrightarrow{1. CrO_{2}Cl_{2}, 2. H_{3}O^{+}}$

Choose the Gattermann-Koch reaction:

The oxidation of benzyl chloride with lead nitrate gives

Which of the following reactions is best for the preparation of an aldehyde from a primary alcohol?

Explain the method of preparation of aldehydes and ketones from acyl chloride (acid chloride) compounds with suitable examples.