Benzaldehyde is obtained from toluene by

 

Given data: we have to find out from above in which reaction benzaldehyde is formed from toluene.

Explanation:

Rosenmund’s reduction: It is the hydrogenation of acyl chloride ion presence of Pd- catalyst.

Cannizzaro reaction: Aldehydes which do not have an α-hydrogen, will undergo self-oxidation and reduction reaction in presence of conc. base.Kolbe’s reaction: In this phenoxide react with $C{O}_2$ to form ortho-hydroxybenzoic acid. Etard reaction: Chromyl chloride oxidizes toluene to a chromium complex, which on hydrolysis gives benzaldehyde.

Hence the correct option is: (D). Etard reaction.