Assertion (A) : Drinking of whisky increases the frequency of urination. Reason (R) : Alcohol intake speeds up the secretion of vasopressin in the body.

Assertion is true: intake of whisky (ethanol) produces a diuretic effect and commonly increases urinary frequency because alcohol promotes water loss through the kidneys [1]. Reason is false: alcohol does not speed up vasopressin (antidiuretic hormone) secretion — it suppresses ADH/vasopressin release. This inhibition of vasopressin reduces water reabsorption in renal collecting ducts and causes increased urine output (diuresis), which explains the increased urination after drinking [2]. Thus the observed diuresis is due to reduced vasopressin action, not an increase in its secretion; R is therefore incorrect as an explanation of A.

Sources

1. [1] https://downloads.regulations.gov/EPA-HQ-OLEM-2018-0830-0009/content.pdf
2. [2] http://www.jci.org/articles/view/106633/files/pdf