Q.
Assertion: Diabetes insipidus is marked by excessive urination and too much thirst of water. Reason: Anti-diuretic hormone (ADH) is secreted by the posterior lobe of pituitary gland.
Antidiuretic hormone (ADH) or vasopressin is secreted by the posterior lobe (Neurohypophysis) of pituitary gland, hyposecretion of ADH results in diabetes insipidus which is characterized by micturating dilute urine several times a day and excessive thirst. So, both Assertion and Reason are correct.