In the conversion of carbonyls to acetals, why is acid necessary for full acetal formation?

• A. Acid is required to protonate the carbonyl oxygen, increasing electrophilicity.
• B. Acid prevents the formation of hemiacetals.
• C. Acid increases the nucleophilicity of the diol.
• D. Acid acts as a catalyst to stabilize the acetal through hydrogen bonding.

Answer: (A)