Final answer:
Magnesium is involved in muscle, bone, and nervous system function. Zinc is necessary for the immune system and cell growth. Iodine is important for thyroid hormone production. Sodium is involved in water balance and nerve signaling.
Step-by-step explanation:
Magnesium (Mg) is found in bone and cells and is involved in muscle, bone, and nervous system function, as well as in many biochemical reactions.
Zinc (Zn) is necessary for the immune system, protein synthesis, and tissue and cell growth.
Iodine (I) is important for the production of thyroid hormones, which regulate metabolism, growth, and development.
Sodium (Na) is found outside the cell and is involved in water balance and nerve signaling.