Complete Guide to CDS physics chemistry biology weightage 2027

The science section in the CDS General Knowledge paper carries a heavy weightage of approximately 30 to 35 questions, translating to 25 to 30 marks out of 100, with biology leading the share followed closely by physics and chemistry, making it a high-scoring priority for aspirants aiming to clear the UPSC cutoff.

Welcome to the ultimate guide by Exam Bhai on mastering the science segment for the Combined Defence Services (CDS) examination. Securing a commission in the Indian Military Academy, Indian Naval Academy, Air Force Academy, or Officers Training Academy requires clearing the rigorous General Knowledge paper. Among all sections, General Science serves as a game-changer because of its predictable syllabus and high return on investment. In this comprehensive manual, we break down the exact physics, chemistry, and biology weightage, analyze past trends, and offer actionable preparation frameworks.

What is the Exam?

The Combined Defence Services Examination (CDS) is conducted twice every year by the Union Public Service Commission (UPSC) for recruitment into the premier defense training academies of India. Aspirants seeking entry must clear a written examination comprising English, General Knowledge, and Elementary Mathematics (for IMA, INA, AFA), or English and General Knowledge (for OTA). The General Knowledge paper evaluates a candidate's awareness of current events, history, geography, polity, economics, and general science up to the 10+2 level. Science forms a core pillar of this paper, demanding conceptual clarity rather than rote memorization. At Exam Bhai, we analyze every shift to help aspirants decode the exact trends, ensuring no marks are left on the table during the exam.

Key Highlights 2026

Staying updated with the latest exam parameters is essential for crafting an effective study roadmap. Here are the core highlights for the upcoming CDS cycle:

• Conducting Body: Union Public Service Commission (UPSC)
• Frequency: Twice a year (CDS I and CDS II)
• Stages of Selection: Written Examination followed by Services Selection Board (SSB) Interview and Medical Examination
• Total Marks (IMA/INA/AFA): 300 Marks (100 each for English, GK, and Maths)
• Total Marks (OTA): 200 Marks (100 each for English and GK)
• General Knowledge Duration: 2 Hours
• Marking Scheme: 0.83 marks awarded for correct answers in IMA/INA/AFA and 1.0 mark in OTA; 0.33 negative marking for incorrect attempts
• Science Weightage Share: Roughly 25% to 30% of the entire General Knowledge paper

Syllabus 2026

The science syllabus for CDS is broad, encompassing fundamental concepts of physics, chemistry, and biology typically taught up to the Class 10 level under standard boards, though UPSC frequently frames analytical application-based questions. Below is the detailed breakdown of topics and their relative sub-weightage:

For chemistry questions involving reactions, candidates must be familiar with standard representations like $CH_4 + 2O_2 ightarrow CO_2 + 2H_2O$. Furthermore, understanding complex organic molecules is crucial. For instance, analyzing the following structure of Acetylsalicylic acid (Aspirin) helps aspirants understand ester functional groups tested in organic chemistry:

CC(=O)Oc1ccccc1C(=O)O

Exam Pattern

The General Knowledge paper is designed to test a candidate's general awareness of the environment and scientific phenomena in everyday life. To master this, you can practice free mock tests for CDS 2027 on Exam Bhai to gauge your speed and accuracy under real exam constraints.

• Mode of Examination: Offline (Pen and Paper based, using OMR sheets)
• Question Type: Multiple Choice Questions (MCQs) with four options
• Total Questions in GK: 100 Questions
• Total Marks: 100 Marks
• Medium of Paper: Bilingual (English and Hindi)
• Sectional Weightage Distribution:
  • Polity & Governance: 15-18 Questions
  • History & National Movement: 15-20 Questions
  • Geography: 18-20 Questions
  • Economy & Current Affairs: 20-25 Questions
  • General Science (Physics, Chemistry, Biology): 30-35 Questions

Eligibility Criteria

Before diving deep into preparation, candidates must verify that they meet all official requirements specified by the commission. According to the guidelines published on the official portal upsc.gov.in, the eligibility parameters are structured as follows:

• Nationality: Must be a citizen of India, a subject of Bhutan, Nepal, or a Tibetan refugee who came over to India before January 1, 1962, with the intention of permanently settling.
• Age Limit & Marital Status:
  • IMA: Unmarried males born between specific dual dates set by the notification (typically ages 19-24).
  • INA: Unmarried males (ages 19-24).
  • AFA: Unmarried males (ages 20-24).
  • OTA (Men & Women): Unmarried/Married men and unmarried women (ages 19-25).
• Educational Qualifications:
  • For IMA and OTA: Graduation degree in any discipline from a recognized university.
  • For INA: Degree in Engineering from a recognized university/institution.
  • For AFA: Degree in Engineering or Graduation with Physics and Mathematics at the 10+2 level.

Application Process

Applying for the examination requires careful adherence to the UPSC guidelines. Here is the step-by-step process:

1. Visit the official UPSC online application portal at upsconline.nic.in.
2. Complete One-Time Registration (OTR) by filling in your basic personal and educational details.
3. Log in using your credentials and select the active CDS Examination notification.
4. Fill out Part I and Part II of the application form, choosing your preferred examination centers.
5. Pay the required application fee of INR 200 (exempted for female candidates and SC/ST candidates) through SBI net banking, Visa/Mastercard, or cash challan.
6. Verify all details and submit the form. Download and print a hard copy of the confirmation page for future reference.

Preparation Strategy

Cracking the science section requires a structured, multi-layered approach. Because UPSC tests conceptual application rather than direct definitions, rote learning will not suffice. To boost your score, we recommend the following strategic steps:

1. NCERT Foundation: Thoroughly read NCERT textbooks from Class 6 to Class 10 for Science. Pay special attention to highlighted boxes, summaries, and exercise questions.
2. Prioritize High-Yield Topics: Focus heavily on human diseases, vitamin deficiencies, photosynthesis, and human organ systems in biology; electricity, optics, and motion laws in physics; and periodic properties, metal extraction, and everyday chemistry in chemistry.
3. Active Practice: Regularly test your concepts by attempting topic-wise quizzes and full-length papers. You can easily practice previous year questions for CDS 2027 on Exam Bhai to identify recurring question patterns.
4. Revise with Error Logs: Maintain a dedicated notebook for formulas, chemical reactions, and biological terms. Review this log weekly to minimize silly mistakes in calculation or recall.

Cut-Off Trends

Understanding previous years' cut-off trends helps set a realistic target score for the written exam. Official data published on upsc.gov.in indicates that the sectional cut-off for each subject is a mandatory 20% minimum, while the overall total cut-off varies by academy:

• OTA (Men): Historically ranges between 95 to 110 marks out of 200.
• OTA (Women): Generally mirrors or stays slightly competitive compared to OTA Men.
• IMA: Ranges between 130 to 145 marks out of 300.
• INA: Ranges between 120 to 135 marks out of 300.
• AFA: Typically the highest, ranging between 145 to 160 marks out of 300.

Given these thresholds, securing at least 20 to 24 marks out of 30 in the General Science section alone gives candidates a massive cushion toward clearing the overall merit threshold.

Frequently Asked Questions

What is the exact weightage of Physics, Chemistry, and Biology in CDS?

Biology typically holds the highest share with 12 to 15 questions, followed by Physics with 10 to 12 questions, and Chemistry with 8 to 10 questions, totaling around 30 to 35 questions in the General Knowledge paper.

Is Class 11 and 12 NCERT science required for CDS?

While standard questions are framed around Class 6 to 10 NCERT levels, UPSC occasionally introduces analytical questions requiring basic awareness of Class 11 concepts, particularly in physics and biology.

Is there negative marking in the CDS General Knowledge paper?

Yes, 1/3rd (0.33) of the marks assigned to a question are deducted for every incorrect answer marked by the candidate.

What is the qualifying sectional percentage required in CDS GK?

Candidates must secure a minimum of 20% marks individually in each subject paper (English, GK, and Mathematics) as mandated by UPSC guidelines.

Can engineering students skip the science section?

Engineering students should not skip science, as the GK paper requires broad familiarity across all three branches, and science offers the most predictable scoring potential compared to unpredictable current affairs.

How can I track my performance improvement in science?

Regular evaluation through targeted mock tests and analyzing your accuracy rates across physics, chemistry, and biology subsections is the best way to monitor growth.