Which of the following acids is a vitamin?

Ascorbic acid is also called as vitamin C. They are found in fish, egg yolks and are synthesized in our body in presence of the sunlight. Thus, option (ii) is correct.

Option (i) is incorrect because aspartic acid is an amino acid.

Option (iii) is incorrect because adipic acid is a dicarboxylic acid.

Option (iv) is incorrect because saccharic acid is also a dicarboxylic acid.