How many papers are conducted in the UPSC Prelims stage and what is their nature?

The UPSC Preliminary Examination consists of two compulsory papers, both of which are conducted on the same day. Both papers are objective-type (Multiple Choice Questions) and serve as a screening mechanism to shortlist candidates for the Mains examination. 

1. General Studies Paper I (Merit-Determining)
Nature: This paper is used to determine the cutoff for qualifying for the Mains. Only the marks scored in this paper are counted for the merit list at the Prelims stage.
Content: It covers broad areas such as Current Affairs, History, Geography, Polity, Economy, Environment, and General Science.
Format: 100 questions, totaling 200 marks.
Marking: Each correct answer earns 2 marks, with a 1/3rd negative marking (0.66 marks) for incorrect answers. 

2. General Studies Paper II (Qualifying - CSAT)
Nature: Officially known as the Civil Services Aptitude Test (CSAT), this paper is strictly qualifying in nature. Marks scored here are not added to the merit list.
Qualifying Criteria: You must score a minimum of 33% (66 out of 200 marks) to pass. If a candidate fails to reach this threshold, their GS Paper I will not be evaluated.
Content: It evaluates aptitude, including reading comprehension, logical reasoning, analytical ability, basic numeracy (Class X level), and decision-making.
Format: 80 questions, totaling 200 marks.
Marking: Each correct answer earns 2.5 marks, with a 1/3rd negative marking (0.83 marks) for wrong answers.