Which of the following chemical elements is essential for the synthesis of the thyroid hormone thyroxine in the human body?

Introduction / Context:
This question relates to basic human physiology and nutrition. The hormone thyroxine, produced by the thyroid gland in the neck, plays an important role in controlling metabolism, growth, and development. A particular chemical element is needed for the synthesis of thyroxine. Deficiency of this element can lead to thyroid disorders such as goitre and hypothyroidism.

Given Data / Assumptions:

• The hormone considered is thyroxine, produced by the thyroid gland.
• We are asked which element is essential for its synthesis.
• Options include potassium, calcium, iodine, sodium, and magnesium.

Concept / Approach:
Thyroxine is often written as T4, indicating that it contains four atoms of iodine in its structure. Another thyroid hormone, triiodothyronine (T3), contains three iodine atoms. The thyroid gland uses iodine from the diet to build these hormones. Without adequate iodine, the gland cannot produce enough hormone and may enlarge, forming a goitre. Therefore, iodine is the essential element for thyroxine synthesis.

Step-by-Step Solution:

Verification / Alternative check:
Biology textbooks and nutrition guides identify iodine deficiency as a major cause of endemic goitre in regions with low natural iodine levels in soil and water. Public health measures such as iodised salt programs are designed to ensure adequate iodine intake for thyroid hormone production. The chemical names and formulas of thyroid hormones explicitly include iodine as part of their structures. All of this confirms that iodine is the correct answer.

Why Other Options Are Wrong:

• Potassium: Important for nerve and muscle function but not specifically required to build the thyroxine molecule.
• Calcium: Essential for bones, teeth, and muscle contraction, but not the key element in thyroxine structure.
• Sodium: Important for fluid balance and nerve function, but not part of thyroxine.
• Magnesium: Involved in enzyme activity and energy production, but not the defining element of thyroid hormones.

Common Pitfalls:
Some students focus on general importance of elements like calcium or sodium and may incorrectly choose them simply because they are well known. It is important to remember the specific connection between iodine and thyroid hormones. Associating the letter I in words like iodine and thyroid helps create a memory link that reduces confusion in multiple choice questions about endocrine and nutritional health.

Final Answer:
The element essential for the synthesis of thyroxine is Iodine.