Final answer:
The element found at 99% inside of the cells of the body is magnesium. It is essential for various cellular functions and is the primary cation in the body's soft tissues. Calcium, sodium, and zinc have different roles and are not as predominantly internal to cells as magnesium.
Step-by-step explanation:
The question you're asking is about which element is found at 99% inside of the cells of the body. The correct answer is d. magnesium.
Notably, magnesium is found primarily inside the cells, where it is involved in many biochemical reactions, including muscle, bone, nervous system functions and cellular metabolism. It's the principal cation in the soft tissues and plays a critical role alongside calcium and phosphorus in bone structure and health. A significant portion of the body's magnesium content is combined with calcium and phosphorus in bone, while the remainder resides in soft tissues and body fluids.
In contrast, elements such as sodium are mainly found outside the cells, whereas calcium is known for its significant presence in bones and teeth as well as for its role in muscle contraction, blood clotting, and nerve function. Zinc, a trace element, is important for various functions but is not predominantly located inside cells.