Which one of the following hormones contains iodine ?

Thyroxine (also called tetraiodothyronine or T4) is an iodinated thyroid hormone; iodine is an essential component incorporated into tyrosine residues to form T3 and T4, so thyroxine contains iodine [2]. Book material explicitly states that iodine is required for synthesis of thyroxin, linking dietary iodine deficiency to goitre, which reflects the thyroid’s dependence on iodine [1]. Detailed physiological sources explain the biochemical formation: iodination of tyrosine residues on thyroglobulin and coupling reactions yield T3 and T4, making iodine an integral part of thyroxine’s structure [2]. The other options are not iodinated: testosterone is a steroid, insulin is a peptide hormone, and adrenaline (epinephrine) is a catecholamine that does not contain iodine [2].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 6: Control and Coordination > Do You Know? > p. 110
2. [2] https://www.ncbi.nlm.nih.gov/books/NBK500006/