UPSC Prelims & Mains :

1) General Studies Paper I

2) General Studies Paper II (more commonly known as Civil Services Aptitude Test or CSAT)

Facts about the IAS prelims you have to know:

Both the papers comprise multiple choice questions.
Both the papers carry negative marks for incorrect answers.
Both the papers are of 200 marks.
GS paper I contains 100 questions.
CSAT paper contains 80 questions.
Both the papers are of 2 hours duration.
Both will be held on the same day with a few hours gap between the papers.
You must score a minimum of 33% in your CSAT to qualify.
GS paper I will be considered qualifying for the IAS Mains exams.
It is compulsory for the candidates to appear in both the papers of Civil Services Prelims Exam for the purpose of valuation. In case a candidate does not appear in both the papers of the IAS prelims exam he/she will be disqualified.
IAS Subject List for Prelims:

GS PAPER I

Current Affairs Analysis and Questions
History of India and Indian National Movement
Indian and World Geography
Physical Geography
Social and Economic Geography
Geography of the World
Indian Polity and Governance
Constitution
Public Policy
Political System
Rights Issues
Panchayati Raj
Economic and Social Development
Sustainable Development
Demographics
Poverty
Social Sector Initiatives
Inclusion
General Issues on Environmental Ecology, Biodiversity and Climate Change
General Science and Technology
CSAT PAPER II
CDS

Comprehension
Interpersonal Skills Including Communication Skills
Logical Reasoning and Analytical Ability
Decision Making and Problem Solving
General Mental Ability
Basic Numeracy
Data Interpretation
English Language Comprehension Skills


UPSC Prelims Syllabus for Paper I – (200 marks)
Duration: Two hours (Counted for the merit rank in the Prelims)

Current events of national and international importance.
History of India and Indian National Movement.
Indian and World Geography – Physical, Social, Economic Geography of India and the World.
Indian Polity and Governance – Constitution, Political System, Panchayati Raj, Public Policy, Rights Issues, etc.
Economic and Social Development Sustainable Development, Poverty, Inclusion, Demographics, Social Sector initiatives, etc.
General issues on Environmental Ecology, Bio-diversity and Climate Change – that do not require subject specialization.
General Science.
UPSC Prelims Syllabus for Paper II- (200 marks)
Duration: Two hours (Not counted for the merit rank in Prelims but a qualifying Paper; just needs 33% marks)

Comprehension.
Interpersonal skills including communication skills.
Logical reasoning and analytical ability.
Decision-making and problem-solving.
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)