The malfunctioning of thyroid gland is due to the deficiency of :

Explanation

Thyroxine, an iodine-containing hormone, is an amino acid, and it is secreted by the thyroid gland. The endocrine hormone that stimulates the thyroid gland to secrete thyroxine ($T_4$) is TSH (Thyroid Stimulating Hormone), also called thyrotropin, which is secreted by thyrotroph cells of the anterior pituitary. When iodine and thyroxine levels in the blood decrease, secretion of TSH from the pituitary increases. Its effect is to stimulate the thyroid to secrete more and more hormones. Due to iodine deficiency in the body, a disease called goitre occurs.