The correct answer is option 1, Aldosterone.

Aldosterone is a hormone produced in the adrenal glands, specifically in the zona glomerulosa of the adrenal cortex. Its primary function is to regulate the balance of electrolytes in the body, particularly sodium and potassium.

Aldosterone acts in the kidneys to increase the reabsorption of sodium ions from the urine back into the bloodstream. This helps to retain sodium in the body, which is important for maintaining the body`s overall fluid balance and blood pressure.

Option 2, Parathormone, is not involved in the retention of sodium ions. Parathormone, also known as parathyroid hormone, is produced by the parathyroid glands and plays a role in regulating calcium and phosphate levels in the body.

Option 3, Somatotropin, is another name for growth hormone, which is primarily involved in the growth and development of bones and tissues. It does not directly influence sodium ion retention.

Option 4, Thyroxin, is a hormone produced by the thyroid gland and is involved in regulating metabolism and energy production in the body. It has no direct role in sodium ion retention.

Therefore, the correct hormone required for the retention of sodium ions by the