The reagent with which both aldehyde and acetone react easily is

The aldehydes which will not form a single Grignard product with one equivalent of Grignard reagent are:
$(a)$ Benzaldehyde
$(b)$ $4$-Formylbenzoic acid
$(c)$ $4$-Methoxybenzaldehyde
$(d)$ $4$-(Hydroxymethyl)benzaldehyde

The major product formed in the following reaction is:

Assertion : Protonation of a carbonyl group increases its electrophilic character.
Reason : Protonation of a carbonyl group involves addition of an electrophile on nucleophilic oxygen.

Which of the following reactions is correctly matched?

Which of the following will give a yellow precipitate with $I_2/NaOH$?