Among the following vitamins, which one is water soluble and therefore must be regularly supplied in the human diet because it is not stored in large amounts in the body?

Introduction / Context:
Vitamins can be broadly classified as water soluble or fat soluble. Water soluble vitamins are not stored in large quantities in the body and need a regular dietary supply, whereas fat soluble vitamins can be stored in tissues such as the liver. This question tests whether you can correctly identify vitamin C as a water soluble vitamin among choices that mainly include fat soluble vitamins A, D and K.

Given Data / Assumptions:
- Vitamins A, D, E and K are fat soluble.- Vitamin C and the B complex vitamins are water soluble.- The options list vitamin A, C, K, D and E.- The question asks which one is water soluble and must be regularly supplied in the diet.

Concept / Approach:
Water soluble vitamins dissolve in water and are transported in the blood plasma. Excess amounts are excreted in urine, so they are not stored extensively in the body. Vitamin C, known as ascorbic acid, is a classic water soluble vitamin that plays roles in collagen synthesis, antioxidant protection and immune function. In contrast, vitamins A, D, E and K are fat soluble and stored in the liver and fatty tissues, which means deficiency takes longer to develop but toxicity is possible if overdosed. Therefore, vitamin C is the correct choice for a water soluble vitamin in this list.

Step-by-Step Solution:
Step 1: Recall that vitamin C and B complex vitamins are water soluble, while A, D, E and K are fat soluble.Step 2: Review the options and identify which one belongs to the water soluble group.Step 3: Note that vitamin C, ascorbic acid, clearly fits this category.Step 4: Confirm that vitamins A, D, E and K are known to be fat soluble and stored in the body.Step 5: Select option B, vitamin C also called ascorbic acid, as the correct answer.

Verification / Alternative check:
Nutrition references list vitamin C with the B vitamins under water soluble vitamins that require regular intake.They also describe how deficiency of vitamin C leads quickly to scurvy if dietary intake is inadequate, reflecting its limited storage.In contrast, fat soluble vitamins remain stored longer, confirming that vitamin C is the only water soluble vitamin among the options.

Why Other Options Are Wrong:
Option A is wrong because vitamin A is fat soluble and stored in the liver, and excess intake can cause toxicity.Option C is wrong because vitamin K is a fat soluble vitamin involved in activation of blood clotting factors.Option D is wrong because vitamin D is fat soluble and involved in calcium and phosphate metabolism.Option E is wrong because vitamin E is a fat soluble antioxidant located mainly in cell membranes and fat stores.

Common Pitfalls:
Students sometimes memorise the list of fat soluble vitamins incorrectly and forget whether vitamin C is water or fat soluble.A simple memory aid is to remember the group of fat soluble vitamins as A, D, E and K, often pronounced as a short sequence, with vitamin C clearly outside that group.Recognising that scurvy, a disease of vitamin C deficiency, develops relatively quickly due to lack of storage also reinforces that vitamin C is water soluble.

Final Answer:
Among the vitamins listed, vitamin C also called ascorbic acid is water soluble and must be regularly supplied in the human diet.