Compound (X) is benzaldehyde (C₆H₅CHO). The correct method to prepare benzaldehyde is through the oxidation of toluene using chromyl chloride (CrO₂Cl₂), known as the Étard reaction.

Step 1: Identify Compound (X)
The structure shows a benzene ring attached to a -CHO group, confirming it as benzaldehyde.

Step 2: Analyze the Options
Option 1: Oxidation of toluene with KMnO₄/KOH gives benzoic acid, not benzaldehyde.
Option 2: Reduction of benzoyl chloride with Pd/BaSO₄ (Rosenmund reduction) gives benzaldehyde.
Option 3: Hydrolysis of benzal chloride (C₆H₅CHCl₂) gives benzaldehyde.
Option 4: Oxidation of toluene with CrO₂Cl₂ (Étard reaction) gives benzaldehyde.

Step 3: Final Answer
Both Option 2 (Rosenmund reduction) and Option 4 (Étard reaction) are valid, but the question asks for the method, and Option 4 is specifically depicted. The Étard reaction is a standard method for preparing benzaldehyde from toluene.

Reaction:
$C_{6} H_{5} C H_{3} + 2 C r O_{2} {Cl}_{2} \to C_{6} H_{5} C H O + other products$

Related Topics

Oxidation of Alkylbenzenes: Toluene can be oxidized to benzoic acid with strong oxidizing agents like KMnO₄, but mild oxidizing agents like CrO₂Cl₂ stop at the aldehyde stage.

Rosenmund Reduction: Reduction of acid chlorides to aldehydes using hydrogen and palladium catalyst poisoned with BaSO₄.

Formulae

Étard Reaction: $R - {CH}_{3} + C r O_{2} {Cl}_{2} \to R - C H O$ (where R is aryl group)

Rosenmund Reduction: $R - C O C l + H_{2} \overset{P d / B a S_{4}}{\to} R - C H O + H C l$