Which of the following hormones is essential for metamorphosis in amphibians?
 

Thyroxine, a thyroid hormone, plays a crucial role in regulating metamorphosis in frogs. During the tadpole stage, thyroid hormones are relatively low. However, as the tadpole develops and prepares for metamorphosis into an adult frog, the thyroid gland begins to produce thyroxine. Thyroxine stimulates various developmental changes, including the reabsorption of the tadpole's tail, the growth of hind limbs, and the remodeling of internal organs, ultimately leading to the transformation into an adult frog.