Final answer:
A nutrient synthesized by the body and necessary for proper body function is not an essential nutrient for maintaining healthy skin because essential nutrients, by definition, cannot be synthesized by the body and must be obtained from the diet.
Step-by-step explanation:
The essential nutrients for healthy skin are those that the body cannot synthesize on its own and thus needs to obtain from the diet. Examples of essential nutrients important for skin health include vitamins A and K, which are fat-soluble and play roles in maintaining connective tissue and blood clotting, respectively. Additionally, zinc plays a crucial role in maintaining healthy skin by contributing to the protection and repair of skin tissues.
The statement that essential nutrients are synthesized by the body and are necessary for proper body function (C.a) is not true. Rather, by definition, a non-essential nutrient can be synthesized by the body in sufficient quantities and thus is not required from the diet. Therefore, a nutrient that is synthesized by the body and is necessary for proper body function is not considered an essential nutrient for maintaining healthy skin or any other bodily function since it does not need to be obtained through diet.