Final answer:
Vitamin D is consumed in its most inactive form, with the skin producing cholecalciferol which is then activated in the liver and kidneys. Vitamin C is the correct water-soluble vitamin among the options provided.
Step-by-step explanation:
We consume significant amounts of vitamin D in its most inactive form. The skin functions as an endocrine organ in the production of the inactive form of vitamin D3, known as cholecalciferol. When cholesterol present in the epidermis is exposed to ultraviolet radiation, it is converted to cholecalciferol, which then enters the blood. This is then processed in the liver and kidneys to become calcitriol, the active form of vitamin D.
As for water-soluble vitamins, the correct answer to which of the following is a water-soluble vitamin is vitamin C. Unlike fat-soluble vitamins, water-soluble vitamins cannot be stored in the body and must be consumed regularly in our diet.