All of the following are fat soluble vitamins except which one?

Introduction / Context:
Vitamins are classified as either fat soluble or water soluble based on how they are absorbed, transported, and stored in the body. This classification has important implications for nutrition, toxicity risk, and deficiency patterns. This question asks which listed vitamin is not fat soluble, meaning it belongs to the water soluble group instead.

Given Data / Assumptions:

Known fat soluble vitamins are A, D, E, and K.
Water soluble vitamins include the B complex group and vitamin C.
The options list vitamins A, C, D, and K.
We assume standard human nutrition definitions.

Concept / Approach:
Fat soluble vitamins are absorbed along with dietary fats, can be stored in body fat and the liver, and include vitamins A, D, E, and K. Water soluble vitamins dissolve in water, are not stored to the same extent, and excess amounts are usually excreted in urine. Vitamin C, also known as ascorbic acid, is a classic water soluble vitamin. Vitamins A, D, and K are all fat soluble and can accumulate in the body. Thus, among the options, vitamin C is the one that is not fat soluble.

Step-by-Step Solution:
Step 1: Recall the list of fat soluble vitamins: A, D, E, and K. Step 2: Note that vitamin C is not in this list and is instead grouped with water soluble vitamins. Step 3: Check the options and identify which one matches the water soluble category. Step 4: Select vitamin C as the exception to the group of fat soluble vitamins.

Verification / Alternative check:
Nutrition guidelines and textbooks consistently refer to vitamins A, D, E, and K as fat soluble and warn that excessive intake of these can lead to toxicity because they accumulate in fat tissues. Vitamin C is emphasized as water soluble, important for collagen synthesis and antioxidant defense, with deficiency leading to scurvy. These descriptions clearly place vitamin C in the water soluble category rather than the fat soluble group.

Why Other Options Are Wrong:
Vitamin A: This is a fat soluble vitamin involved in vision, immune function, and cell growth.
Vitamin D: It is fat soluble and important for calcium metabolism and bone health.
Vitamin K: This fat soluble vitamin is essential for normal blood clotting mechanisms.

Common Pitfalls:
Some learners memorize the full list of vitamins without grouping them by solubility, which can make it easy to forget which are fat soluble. A simple memory aid is to remember the four fat soluble vitamins as A, D, E, and K, sometimes recalled with a short phrase made from their letters. Any other vitamin, including vitamin C and all B vitamins, will be water soluble. Using such tricks can prevent confusion during exams.

Final Answer:
Among the options, the vitamin that is not fat soluble is vitamin C, which belongs to the water soluble group.