Which of the following is NOT a fat-soluble vitamin?

The reasoning for identifying the option related to vitamin B as not being a fat-soluble vitamin is based on the fundamental characteristics of vitamins and their solubility. Fat-soluble vitamins include A, D, E, and K, which dissolve in fats and oils and can be stored in the body's fatty tissues and liver.

Vitamin B, on the other hand, refers to a group of water-soluble vitamins that primarily includes B1 (thiamine), B2 (riboflavin), B3 (niacin), B5 (pantothenic acid), B6 (pyridoxine), B7 (biotin), B9 (folate), and B12 (cobalamin). These vitamins do not dissolve in fats and are instead soluble in water, which means they must be consumed more regularly in the diet because the body does not store excess amounts.

In summary, vitamin B is classified differently because of its water solubility, making it distinct from the fat-soluble vitamins A, D, and E, which the body can store for later use.