What Are The Optional Subjects For IAS Mains Exam? The UPSC conducted IAS exam has three phases: the prelims, the mains and the interview. The Prelims has two objective question papers. The Mains has nine descriptive question papers, of which two are optional. For most IAS aspirants, deciding which optional subject to choose is confusing as the two combined are worth 500 marks. Therefore, they play a critical role in the final tally of scores. Here is a list of all the optional subjects you can pick from for the IAS Mains Exam: --> Botany --> Chemistry --> Psychology --> Sociology --> Statistics --> Agriculture --> Anthropology --> Zoology --> Philosophy --> Physics --> Economics --> Geography --> Geology --> History --> Law --> Management --> Mathematics --> Medical Science --> Civil Engineering --> Electrical Engineering --> Mechanical Engineering --> Commerce & Accountancy --> Public Administration --> Animal Husbandry and Veterinary Science --> Political Science & International Relations