UPSC Prelims consists of two paper, each paper consists of 200 marks GS Paper -1 has the following topics-

History(History of India and Indian Freedom Struggles)

Geography(Geography of India and Concept of Physical Geography)

Polity(Indian Polity and Governance issues)

Economy(Indian Economy and Social Development)

Environment and Ecology(Principles of Environment and Ecology)

General Science(Physics, Chemistry, Biology and Technology)

Current Events(It covers all the events of National and International Importance)

General Studies- Paper II(CSAT) is of qualifying nature and consists of the following-

Reading Comprehension

Interpersonal skills including communication skills;

Logical reasoning and analytical ability

Decision making and problem-solving ability

General mental ability

Basic numeracy (numbers and their relations, orders of magnitude, etc.) (Class X level), Data interpretation (charts, graphs, tables, data sufficiency etc. - Class X level)

English Language Comprehension skills (Class X level).

Questions relating to English Language Comprehension skills of Class X level (last item in the Syllabus of Paper-II) will be tested through passages from English language only without providing Hindi translation thereof in the question paper.

Mains Syllabus consists of the following

Essay Paper - 250 marks

GS Paper I(Indian Heritage and Culture, Indian History, World History, World Geography, Indian Society, Important Geo-physical phenomena) - 250 marks

GS Paper II (Governance, Indian Constitution, Polity, Social Justice and International relations, Welfare Schemes, Statutory, regulatory and quasi-judicial bodies, Role of civil services in a democracy, India’s relation with neighbour countries, International institutions) - 250 marks

GS Paper III(Technology,Economic Development, Bio diversity,Environment, Indian Economy and its various sectors,Government Budgeting,Land Reforms,Inclusive Growth,Security and Disaster Management - 250 marks

GS Paper IV(Ethics and Human Interface,Attitude,Aptitude,Emotional Intelligence,Public/Civil service value,Probity in Governance,Case study on above topics) - 250 marks

Indian Language Paper(Comprehension of given passages,Précis Writing,Usage and Vocabulary,Short Essays,Translation from English to the Indian language and vice-versa) - 300 marks

English(Comprehension of given passages,Précis Writing,Usage and Vocabulary,Short Essays) - 300 marks

Optional Paper I - 250

Optional Paper II - 250 marks

Now, coming to the list of options -

• Agriculture
• Animal Husbandry and Veterinary Science
• Anthropology
• Botany
• Chemistry
• Civil Engineering
• Commerce and Accountancy
• Economics
• Electrical Engineering
• Geography
• Geology
• History
• Law
• Management
• Mathematics
• Mechanical Engineering
• Medical Science
• Philosophy
• Physics
• Political Science and International Relations
• Psychology
• Public Administration
• Sociology
• Statistics
• Zoology

Literature of any one of the languages such as Assamese, Bengali, Bodo, Dogri, Gujarati, Hindi, Kannada, Kashmiri, Konkani, Maithili, Malayalam, Marathi, Oriya, Punjabi, Sanskrit, Santhali, Sindhi, Tamil, Telugu, Urdu, English.

Your optional should depend largely on your interest because you have to spend a considerable amount of time studying it, covering optional for UPSC is nothing short of graduation level course, yes! that's a reality you have to study so much as you can see how much you have to write in Mains Paper.You can choose any of the science subjects or even medicine for that matter.