The NDA (National Defence Academy) and CDS (Combined Defence Services) exams test candidates on basic concepts of General Science, including foundational Chemistry. Although the questions are simple, they require clear understanding, quick recall, and conceptual clarity.
Topics like Atomic Structure and Redox Reactions form the building blocks for many questions asked in General Science sections of NDA/CDS examinations.

Topic 1: Atomic Structure

Introduction

Atomic Structure is the study of the basic building block of matter—the atom. Understanding atoms, their components, and their behavior helps students grasp the fundamentals of all chemical reactions. At the Class 8 level, concepts are simple but extremely important for NDA/CDS examinations.

Subtopics

1. Definition of an Atom
   • Smallest unit of matter
   • Cannot be further divided by chemical means
2. Constituents of an Atom
   • Protons: positively charged
   • Neutrons: neutral
   • Electrons: negatively charged
3. Atomic Number and Mass Number
   • Atomic number = number of protons
   • Mass number = protons + neutrons
4. Nucleus and Electron Shells
   • Dense central nucleus containing protons and neutrons
   • Electrons revolve in shells or energy levels (K, L, M…)
5. Models of the Atom (basic understanding)
   • Dalton’s Atomic Theory
   • Thomson’s model
   • Rutherford’s model
   • Bohr’s model
6. Isotopes and Ions
   • Isotopes: atoms of same element with different mass
   • Ions: charged atoms (cation/anion)

Topic 2: Redox Reactions

Introduction

Redox reactions are chemical changes in which oxidation and reduction occur simultaneously. Even at the Class 8 level, understanding this concept is important since many everyday processes—rusting, respiration, combustion—are examples of redox reactions.

Subtopics

1. Oxidation
   • Addition of oxygen
   • Removal of hydrogen
   • Loss of electrons
2. Reduction
   • Removal of oxygen
   • Addition of hydrogen
   • Gain of electrons
3. Oxidizing and Reducing Agents
   • Oxidizing agent: causes oxidation (gets reduced)
   • Reducing agent: causes reduction (gets oxidized)
4. Redox in Daily Life
   • Rusting of iron
   • Respiration (glucose oxidation)
   • Combustion of fuels
   • Photosynthesis (reduction of CO₂)
5. Simple Redox Equations (class 8 level)
   • Examples of reactions involving gain or loss of oxygen/hydrogen.

Conclusion

Atomic Structure and Redox Reactions together form a strong conceptual base in Chemistry. For the NDA/CDS 1 2026 exam, having clarity in these topics ensures accuracy in General Science MCQs. Since questions focus on basic definitions, principles, and examples, mastering these concepts will significantly boost confidence and performance in the exam.