Which one of the following is essential for thyroid gland to make thyroxin?

Iodine is an essential trace element required by the thyroid gland for the synthesis of thyroxine (T4) and triiodothyronine (T3) [1]. The process begins when dietary iodide is actively transported into the thyroid follicular cells and then into the colloid [1]. Within the colloid, the enzyme thyroid peroxidase facilitates the oxidation of iodide and its subsequent binding to tyrosine residues on the protein thyroglobulin, a process known as organification. This results in the formation of monoiodotyrosine (MIT) and diiodotyrosine (DIT), which then couple to form T4 and T3 [1]. A deficiency in iodine intake prevents the gland from producing sufficient thyroxine, which can lead to the development of goitre, characterized by a swollen neck [1]. While NaCl (table salt) is often the vehicle for iodine delivery (iodized salt), iodine itself is the critical chemical component for hormone production [1].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 6: Control and Coordination > Do You Know? > p. 110