Step 1: Understanding the Question:
We need to identify which carbonyl compound reacts with a Grignard reagent (\( RMgX \)) to produce a tertiary (\( 3^\circ \)) alcohol after acidic hydrolysis. Step 2: Detailed Explanation:
1. Formaldehyde (Methanal): Reacts with \( RMgX \) to give a primary (\( 1^\circ \)) alcohol.
2. Higher Aldehydes (Ethanal, Propanal): React with \( RMgX \) to give secondary (\( 2^\circ \)) alcohols.
3. Ketones (Propanone): React with \( RMgX \) to give tertiary (\( 3^\circ \)) alcohols.
Reaction for Propanone:
\[ CH_3COCH_3 + RMgX \rightarrow R-C(CH_3)_2-OMgX \xrightarrow{H_2O/H^+} R-C(CH_3)_2-OH \] Step 4: Final Answer:
Propanone (a ketone) yields a tertiary alcohol.