Which of the following vitamins is not fat-soluble?

Vitamin C is classified as a water-soluble vitamin, making it distinct from the other options listed, which are all fat-soluble vitamins. Fat-soluble vitamins, including A, D, and K, are absorbed along with dietary fat and can be stored in the body's fatty tissue and the liver for later use. In contrast, water-soluble vitamins like vitamin C are absorbed directly into the bloodstream and are not stored in significant amounts, which means they need to be consumed more regularly to maintain adequate levels in the body.

Vitamin C plays a crucial role in various bodily functions, including serving as an antioxidant, supporting the immune system, and aiding in the synthesis of collagen. Since it is readily excreted in urine, it requires consistent intake to prevent deficiency, which is a key characteristic that sets it apart from fat-soluble vitamins, which have a much longer shelf life within the body.