YES. Zoology is the best and easy optional if u have a background in zoology or life sciences.
Zoology also is applied subject in science so it also can help you to understand some questions related to science and technology.
In UPSC pre there are roughly 20– 25 question are originating from biology and condition which are also a part of zoology.
So if you have good knowledge of zoology and have done graduation in zoology then you can go with zoology as your optional in civil.