BIOMOLECULES AND ENZYMES

Detailed explanation-1: -Guanine is is not a vitamin but it is a nitrogenous base. Niacin is called as vitamin B3, riboflavin is vitamin B2 and thiamine is vitamin B1.

Detailed explanation-2: -Vitamin A is available in dietary supplements, usually in the form of retinyl acetate or retinyl palmitate (preformed vitamin A), beta-carotene (provitamin A), or a combination of preformed and provitamin A.

Detailed explanation-3: -Vitamins do not occur naturally in rocks and minerals. This is because vitamins are organic in nature which means they are derived from living organisms and not inanimate matter like rocks. Vitamins are organic compounds which are needed by the human body in small amounts.