Answer:
The correct answer is- iodine
Step-by-step explanation:
Thyroid glands is an important endocrine gland of the body which release hormone called thyroid hormone in the blood. It plays an important role in metabolism, brain development, and function, muscle control, etc.
The active form of thyroxine is triiodothyronine and the formation of thyroid hormone requires the availability of iodine. Four iodine atoms are present in thyroxine and 3 is present in triiodothyronine. Without iodine, they can not be produced.
Therefore iodine is the essential element that is required for the manufacturing of thyroxine and triiodothyronine.