Complete Guide to CDS chemistry and physics important topics 2026

Mastering CDS chemistry and physics important topics is essential for clearing the General Knowledge paper in the Combined Defence Services examination, where science questions form a high-scoring cornerstone for aspirants aiming to secure a prestigious commission in the Indian Armed Forces.

What is the Exam?

The Combined Defence Services (CDS) Examination is conducted twice every year by the Union Public Service Commission (UPSC) for recruitment into the Indian Military Academy (IMA), Indian Naval Academy (INA), Air Force Academy (AFA), and Officers Training Academy (OTA). For candidates targeting the upcoming sessions, understanding the core structure of the General Knowledge paper—specifically the science components—is vital. Physics and Chemistry together contribute a substantial share of questions in the General Knowledge section, testing both conceptual clarity and practical application. At ExamBhai, we guide aspirants through a rigorous, structured approach to master these subjects effectively, ensuring you stay ahead of the competition.

Key Highlights 2026

• Conducting Body: Union Public Service Commission (UPSC)
• Exam Frequency: Twice a year (CDS I and CDS II)
• Stages of Selection: Written Examination followed by SSB Interview and Medical Examination
• Paper Name: General Knowledge (for IMA, INA, AFA)
• Total Marks for GK: 100 Marks (2 hours duration)
• Science Weightage: Approximately 20 to 30 questions combined from Physics, Chemistry, and Biology
• Marking Scheme: Negative marking of 0.33 marks for every incorrect answer
• Language Medium: Bilingual (English and Hindi)

Syllabus 2026

The General Knowledge syllabus for CDS is broad, but science questions are generally designed around the 10th-standard CBSE curriculum, focusing on everyday observations and scientific principles. Below is the detailed breakdown of important physics and chemistry topics.

To test your preparation levels on these specific topics, you can practice free mock tests for CDS 2027 on ExamBhai.

Exam Pattern

The written examination pattern varies slightly depending on whether a candidate is opting for the OTA or the permanent commission academies (IMA, INA, AFA).

The General Knowledge paper consists of 120 objective-type multiple-choice questions carrying a total of 100 marks. Science questions typically range between 25 to 30 percent of the paper, making physics and chemistry high-yield areas. To analyze previous trends and pattern shifts, you can evaluate past papers and attempt sectional quizzes for CDS 2027 on ExamBhai.

Eligibility Criteria

According to official guidelines published on the UPSC portal (upsc.gov.in), candidates must fulfill specific nationality, age, educational qualification, and marital status criteria:

• 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.
• Age Limit: Varies by academy. IMA requires unmarried males aged 19-24 years; AFA requires 20-24 years; INA requires unmarried males 19-22 years; OTA requires unmarried men and women aged 19-25 years.
• Educational Qualification: For IMA and OTA, a recognized graduation degree in any discipline. For INA, a degree in Engineering from a recognized university. For AFA, a degree in Engineering or graduation with Physics and Mathematics at the 10+2 level.
• Physical Standards: Candidates must be physically fit according to guidelines specified by the official recruiting authority.

Application Process

The application process for CDS is conducted entirely online through the official UPSC portal.

• Step 1: Visit the official UPSC website (upsc.gov.in) or the active examination portal.
• Step 2: Complete One-Time Registration (OTR) by providing basic personal and academic details.
• Step 3: Log in using your credentials and select the CDS examination notification.
• Step 4: Fill in the application form, choosing your preferred examination centers carefully.
• Step 5: Upload scanned copies of your photograph and signature in the prescribed format.
• Step 6: Pay the requisite application fee (exempted for female candidates and SC/ST category candidates).
• Step 7: Submit the form and download a final printout of the confirmation page for future reference.

Preparation Strategy

Cracking the CDS General Knowledge paper requires a balanced mix of conceptual understanding and regular revision. Because chemistry and physics questions frequently test practical applications, rote memorization will not suffice.

• Build NCERT Foundations: Thoroughly read class 9th and 10th science textbooks to clear fundamental concepts in kinematics, optics, and chemical bonding.
• Focus on Numerical Problem-Solving: Practice basic physics formulas such as (v = u + at), (F = ma), and electrical power calculations (P = VI).
• Master Chemical Reactions: Understand how compounds react, such as the synthesis of organic structures. For instance, consider the organic reaction where Salicylic acid reacts with acetic anhydride to form Aspirin:

CC(=O)Oc1ccccc1C(=O)O

• Solve Previous Year Papers: Analyze the last 5 to 10 years of UPSC question papers to identify recurring concepts like mirror formulas, lens makers formulas, and pH calculations.
• Take Timed Tests: Speed and accuracy are vital when managing a 120-question paper in 120 minutes. You can access comprehensive study modules and practice free mock tests for CDS 2027 on ExamBhai to build exam temperament.

Cut-Off Trends

Cut-off marks for the CDS examination vary across different academies based on paper difficulty and the total number of vacancies. Based on historical data available via official UPSC archives (upsc.gov.in), the sectional cut-off for the written exam typically hovers around 20 percent marks in each subject, while the overall qualifying marks range between these approximate thresholds:

• IMA: 130 - 145 marks out of 300
• INA: 115 - 130 marks out of 300
• AFA: 140 - 155 marks out of 300
• OTA: 100 - 115 marks out of 200

Aspirants must score well above the minimum qualifying threshold in the General Knowledge paper to maximize their cumulative score before the SSB interview stage.

Frequently Asked Questions

1. How many questions from physics and chemistry are usually asked in the CDS GK paper?

Typically, out of 120 questions in the General Knowledge section, around 25 to 30 questions are asked from the combined domains of Physics, Chemistry, and Biology, with physics and chemistry accounting for roughly 15 to 18 questions.

2. Is the CDS science syllabus based on 11th and 12th standard levels?

No, the standard of questions for physics and chemistry in CDS is generally matriculation (10th standard) level, focusing on conceptual clarity and daily-life applications rather than advanced derivations.

3. What are the most important physics topics for CDS?

Optics (reflection, refraction, lenses), Mechanics (laws of motion, gravitation, work and energy), and Electricity & Magnetism are the most frequently tested physics units in the exam.

4. How should I prepare chemical equations and formulas for CDS?

Focus on balanced chemical reactions, understanding oxidation-reduction processes, calculating valencies, and knowing standard pH values of common substances used in daily life.

5. Is there negative marking in the CDS General Knowledge paper?

Yes, there is a negative marking of 0.33 marks for every question answered incorrectly in the objective-type written examination.

6. Where can I practice topic-wise mock tests for CDS 2027 science preparation?

You can practice structured mock tests and chapter-wise question banks directly on dedicated portals like ExamBhai to evaluate your speed and accuracy.