Final answer:
Iodine treats goiter and thyroid disease by providing the essential nutrient required for the synthesis of thyroid hormones.
Step-by-step explanation:
The correct answer is d. Iodine.
Iodine treats goiter and thyroid disease because it is an essential nutrient required for the synthesis of thyroid hormones. The thyroid gland uses iodine to produce hormones such as thyroxine (T4) and triiodothyronine (T3), which regulate metabolism and various other body functions.
In cases of hypothyroidism caused by iodine deficiency, giving iodine can help alleviate the symptoms and restore normal thyroid function.