Which of the following acids is a vitamin?

We need to identify which acid is a vitamin.

Analyzing each option:

(A) Adipic acid - This is a dicarboxylic acid ($$HOOC(CH_2)_4COOH$$) used in nylon production. It is NOT a vitamin.

(B) Ascorbic acid - This is Vitamin C, an essential nutrient required for tissue repair and enzymatic production.

(C) Saccharic acid - This is glucaric acid, a sugar acid. It is NOT a vitamin.

(D) Aspartic acid - This is an amino acid. It is NOT a vitamin.

The correct answer is Option 2: Ascorbic acid (Vitamin C).