Step 1: Understanding Thyroxine Hormone
Thyroxine is a hormone produced by the thyroid gland in the human body. It plays an important role in regulating metabolism and growth.
Step 2: Role of Iodine in Thyroxine Synthesis
Iodine is an essential element for the production of thyroxine. The thyroid gland combines iodine with the amino acid tyrosine to form thyroxine. Without sufficient iodine, the thyroid cannot produce enough thyroxine, which leads to various health issues such as goiter.
Step 3: Why the Other Options are Incorrect
- (A) Chlorine: Chlorine does not play a role in the synthesis of thyroxine.
- (C) Fluorine: Fluorine is not involved in thyroxine synthesis either.
- (D) None of these: This option is incorrect because iodine is required for thyroxine synthesis.
Thus, the correct answer is option (B) Iodine.
Match the hormone with its site of production:

| Hormones | Chemical Nature |
|---|---|
| A) Insulin | IV) Protein |
| B) Estrogen | I) Steroid |
| C) Oxytocin | II) Peptide |
| D) Thyroxine | III) Amine |