An organic compound \('X'\) on treatment with methyl magnesium bromide gives a compound \('Y'\) which on hydrolysis gives ethanol. The compound \('X'\) is:

\(HCHO\)

The correct answer is option 3. \(HCHO\).

The reaction described involves the Grignard reaction, where an organic compound (in this case, 'X') reacts with an organomagnesium compound (in this case, methyl magnesium bromide, \(CH_3MgBr\)) to form a new compound (in this case, 'Y'). This intermediate compound 'Y' then undergoes hydrolysis to give ethanol (\(CH_3CH_2OH\)). Formaldehyde can react with methyl magnesium bromide to form a primary alcohol, methanol (\(CH_3OH\)), which upon hydrolysis will give ethanol.