Step 1: Understand the definition of a vitamin.
A vitamin is an organic compound that is essential for normal growth and nutrition and is required in small quantities in the diet because it cannot be synthesized by the body.
Step 2: Identify the given acids.
(1) Adipic acid: A dicarboxylic acid used in the production of nylon.
(2) Aspartic acid: An amino acid, a building block of proteins.
(3) Ascorbic acid: Also known as Vitamin C, an essential nutrient.
(4) Saccharic acid: An oxidation product of sugars.
Step 3: Determine which acid is a vitamin.
Ascorbic acid is the chemical name for Vitamin C, which is an essential vitamin required for various bodily functions, including immune system support and collagen synthesis.
Step 4: Conclude the answer.
Therefore, the correct answer is (3) Ascorbic acid.