Explanation:

- Metamorphosis in amphibians, such as frogs, is primarily controlled by Thyroxine.

- Correct Answer: Option 3 - Thyroxine

- Thyroxine is a hormone produced by the thyroid gland. It plays a crucial role in the growth and development, specifically in turning tadpoles into frogs.

- Option 1: Melatonin

- Melatonin is primarily involved in regulating sleep-wake cycles, not in metamorphosis.

- Option 2: Adrenalin

- Adrenalin, or adrenaline, is involved in the fight-or-flight response. It’s not related to metamorphosis processes.

- Option 4: Insulin

- Insulin regulates blood sugar levels and is not involved in the metamorphosis of frogs.