Final answer:
The thyroid hormone is synthesized in the thyroid gland, which is located in the neck. Iodine is crucial for its synthesis.
Step-by-step explanation:
The thyroid hormone is synthesized in the thyroid gland, which is located in the neck just below the larynx and in front of the trachea. The hormone synthesis process requires iodine, which is taken up by the thyroid gland through an active transport mechanism. The enzyme thyroperoxidase converts iodide to active iodine, which is crucial for the synthesis of thyroid hormones.