Which one of the following vitamins is water-soluble?

The correct answer identifies that vitamin A is classified as a fat-soluble vitamin, which is not accurate when determining the water-soluble vitamins. Water-soluble vitamins include those that dissolve in water, such as the B-vitamins and vitamin C. These vitamins are easily absorbed by the body and are not stored in large amounts, requiring regular intake through diet.

Focusing on the characteristics of the vitamins listed, vitamin A is essential for vision and immune function, but it is fat-soluble and therefore requires dietary fats for absorption. Similarly, vitamins D and E are also fat-soluble. Vitamin D is crucial for calcium metabolism and bone health, while vitamin E acts as an antioxidant. Vitamin K plays a vital role in blood clotting and bone metabolism, and like the others mentioned, it is also classified as fat-soluble.

In summary, when classifying vitamins, it's important to differentiate between water-soluble and fat-soluble vitamins accurately. The water-soluble vitamins are primarily vitamin C and the B-complex vitamins, whereas vitamins A, D, E, and K are all fat-soluble.