Question

Hormone which controls day and night/day biological clock

Answer 1

A hormone called Melatonin secreted by the Pineal Gland which is located in the epithalamus of the brain. Melatonin is responsible for diurnal rhythm (sleep-wake cycle).

Answer 2

These are mostly hypothalamus hormones the melatonin is also responsible for day and night balance in the pituitary gland also controls the hormonal the oxytocin is also responsible for the biological clock