Product 'A' is:

Salicylic acid

Salicylic acid is an important industrial organic compound that can be derived from phenol through two different types of reactions. It contains the same structure as that of phenol with an additional carboxylic acid group (COOH) placed at the ortho position (adjacent position) of the hydroxyl group of phenol.

The reaction above is Kolbe-Schmidt reaction.

Kolbe-Schmitt reaction: This reaction involves the conversion of acidic phenol into a phenoxide ion in presence of sodium hydroxide base. This is followed by the attack of phenoxide ion of the electrophilic carbon dioxide gas resulting in a carboxylate group getting attached at the ortho position. The reaction ends with a mild acidic hydrolysis that gives salicylic acid.

Thus it is a base-facilitated carboxylation of phenol.