Excretion

ADH (Antidiuretic Hormone), also called vasopressin, plays a vital role in water balance by promoting reabsorption of water from the kidney tubules into the blood. This hormone reduces the volume of urine and helps the body retain water.
When there is a deficiency of ADH, the kidneys are unable to reabsorb sufficient water. This leads to the production of a large volume of dilute urine, a condition known as diuresis. This is characteristic of disorders like diabetes insipidus.
- Option (2) is incorrect because ADH deficiency increases urine volume, not decreases it.
- Option (3) is incorrect because ADH primarily regulates water, not electrolyte reabsorption.
- Option (4) is incorrect because ADH is not involved in calcium regulation.
Thus, the correct answer is Diuresis.