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

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

NaCl
KCl
Cholesterol
Iodine
This question was previously asked in
UPSC CDS-1 – 2023
Iodine is an essential trace element required by the thyroid gland to synthesize thyroid hormones, namely thyroxine (T4) and triiodothyronine (T3).
Iodine atoms are incorporated into the structure of the thyroxine and triiodothyronine molecules. Deficiency of iodine can lead to impaired thyroid hormone production, resulting in conditions like goiter and hypothyroidism.
The thyroid gland actively accumulates iodide ions from the blood. The synthesis of thyroid hormones involves the iodination of tyrosine residues on the protein thyroglobulin.