Step 1: Understand the question.
Toluene is treated with chromyl chloride ($CrO_2Cl_2$), then hydrolysed, and benzaldehyde forms. We must name this reaction.
Step 2: Spot the change happening.
The $CH_3$ group on the benzene ring of toluene turns into a $CHO$ group. This is a controlled oxidation of a side methyl group to an aldehyde.
Step 3: Recall the Etard reaction.
The Etard reaction uses chromyl chloride to oxidise the methyl group of toluene, giving a brown complex that is then hydrolysed to benzaldehyde.
Step 4: Match the reagent.
Since the reagent here is exactly chromyl chloride and the product is benzaldehyde, this fits the Etard reaction perfectly.
Step 5: Rule out the others.
Stephen reduction turns a nitrile into an aldehyde. Rosenmund uses $H_2/Pd\text{-}BaSO_4$ on an acid chloride. Wolff-Kishner removes a carbonyl. None match.
Step 6: Choose the answer.
The reaction is the Etard reaction, which is option 2.
\[ \boxed{\text{Etard reaction}} \]
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