Simple process of diffusion is sufficient for excretion in:

Explanation

The correct answer is Hydra. Hydra is a simple multicellular organism that lacks specialized organs for excretion. It relies on the process of diffusion to eliminate waste products directly through its body surface. This is sufficient due to its simple body structure and the aquatic environment it lives in.Earthworms, Planaria, and Cockroaches, on the other hand, have more complex bodies and require specialized structures for excretion. Earthworms use nephridia, Planaria use protonephridia, and Cockroaches rely on Malpighian tubules, all of which are more complex systems than simple diffusion.