The tadpoles of a frog represent which stage of metamorphosis?

Metamorphosis is the transformation of the larva into an adult through drastic changes.

The development in frogs is indirect i.e., the eggs after hatching undergo an intermediate stage before developing into an adult.

As the eggs hatch, they develop into small tadpoles also known as larvae. The larvae then transform into adult frogs capable of jumping and swimming. 

Thus, the tadpoles of a frog represent the larval stage of metamorphosis.