The vitamin which can be most easily synthesised in human body is
A. Vitamin D
B. Vitamin C
C. Vitamin B
D. Vitamin K

Hint: There are a total fourteen vitamins that are essentially required in humans. On the idea of their solubility, these vitamins are classified into two main groups. First is Water soluble vitamins. These include 10 kinds of vitamins. Another one is Fat soluble vitamins. These include 4 kinds of vitamins.Among these 14 vitamins, Humans can synthesize Vitamin D3 & Niacin.

Complete step by step answer:
Let's discuss the option and find the correct answer .
A. Vitamin D: There are few vitamins that cannot be synthesized and must be supplied to the body as dietary supplements. The vitamin which will be synthesized by the physical body is vitamin D . Vitamin D is synthesized by the human skin when exposed to sunlight. Hence option A is correct .
B. Vitamin C: Vitamin C is employed within the maintenance of bones, muscle, and blood vessels. It also assists in the formation of collagen. It helps the body absorb iron. Hence option B is incorrect .
C. Vitamin B: B-complex vitamin plays an important role in maintaining healthiness and well-being. As the building blocks of a healthy body, B vitamins have an immediate impact on your energy levels, brain function, and cell metabolism. Hence option C is incorrect.
D. Vitamin K: Vitamin K is the component naturally synthesised in the human small intestine by bacteria present there. vitamin K helps in the blood clotting process without intake from outside. Hence option K is incorrect .
Hence option A: Vitamin D is the correct answer.

Note: Vitamins are essential for the traditional growth and development of a multicellular organism.Vitamin C is often synthesized by most animals except humans, monkeys, guinea pigs, indian fruit bats, some birds and fishes. Therefore, humans require vitamin C in their diet.