Zoology is popular among many IAS aspirants as an optional subject in Mains examinations UPSC. Here in this article, you will get entire details about how is zoology for optional for UPSC. In UPSC IAS examination there are three stages namely- Prelims, Mains and Interview. In UPSC Mains, a student has to select an optional subject from available list and zoology is also a choice among many science graduates.