A chemistry plan for NDA

Chemistry is the quietly reliable part of NDA General Knowledge. The NDA & NA (II) 2026 notification gives it an approximate weightage of 15% of the GK section. With GK worth 400 marks and questions carrying 4 marks each in recent papers, that is roughly 60 marks, or about 15 questions. It is more than general science or current events, and nearly all of it comes from Class 8–10 science.

The questions are short. You will rarely calculate anything longer than a molecular mass. What they test is precision: the exact formula of washing soda, which gas turns lime water milky, why a scratched galvanised sheet still does not rust, which of four statements about graphite is wrong. A candidate who has learnt school chemistry carefully, and not just read it, picks up these marks in seconds.

What the syllabus actually lists

The chemistry section of the official syllabus is short. In plain terms it covers:

• physical and chemical changes;
• elements, mixtures and compounds; symbols, formulae and simple chemical equations; the laws of chemical combination (without numerical problems);
• properties of air and water;
• preparation and properties of hydrogen, oxygen, nitrogen and carbon dioxide;
• oxidation and reduction;
• acids, bases and salts;
• carbon and its different forms;
• fertilisers, natural and artificial;
• the materials used to make soap, glass, ink, paper, cement, paints, safety matches and gunpowder;
• elementary ideas of atomic structure, atomic, equivalent and molecular weights, and valency.

Two things stand out. First, the "materials" line is unusual. Most school courses skip it, so most candidates skip it too, yet it is one page of notes and a few sure marks. Second, questions do not stay strictly inside these lines. Metals and non-metals, the periodic table and carbon compounds appear regularly, because they sit underneath the listed topics in Class 9–10 NCERT. Prepare the full Class 10 chemistry course, then add the syllabus extras.

How questions are asked

Statement questions are where marks leak. Each statement is usually true except for one word such as "all", "only" or "always". Read them as a checker hunting for that word, not as a reader nodding along.

The order to study in

Start with matter, elements, compounds and mixtures and then physical and chemical changes, because every later topic uses their vocabulary.

A six-week plan

Chemistry sits well alongside physics. Forty-five minutes, four days a week, is enough if you are consistent. Each session: read the NCERT section, write half a page of notes (formulas, one balanced equation, three everyday uses), then do 15 MCQs. Log every mistake with the reason you made it, not just the right answer.

Worked NDA-style MCQs

Q1. The chemical formula of washing soda is:
(a) NaHCO₃ (b) NaOH (c) CaOCl₂ (d) Na₂CO₃·10H₂O

NaHCO₃ is baking soda, NaOH is caustic soda and CaOCl₂ is bleaching powder. Every wrong option is a real compound, which is typical of NDA. Answer: (d).

Q2. The molecular mass of calcium carbonate, CaCO₃ (Ca = 40, C = 12, O = 16), is:
(a) 68 (b) 84 (c) 100 (d) 116

40 + 12 + (3 × 16) = 40 + 12 + 48 = 100. Answer: (c).

Q3. The head of a safety match contains:
(a) potassium chlorate (b) red phosphorus (c) white phosphorus (d) sodium chloride

The head carries potassium chlorate and antimony trisulphide; the red phosphorus is on the side of the box. That separation is what makes the match "safe". Answer: (a).

Q4. Which gas turns lime water milky?
(a) oxygen (b) hydrogen (c) carbon dioxide (d) nitrogen

Ca(OH)₂ + CO₂ → CaCO₃ + H₂O. The insoluble calcium carbonate is the milkiness. Answer: (c).

Q5. Consider these statements: 1. Diamond is a good conductor of electricity. 2. Graphite is used as a lubricant. 3. Both are forms of carbon. Which are correct?
(a) 1 and 2 (b) 2 and 3 (c) 1 and 3 (d) 1, 2 and 3

Diamond has no free electrons and does not conduct. Graphite's layers slide over one another. Answer: (b).

Q6. Gunpowder is a mixture of:
(a) potassium nitrate, charcoal and sulphur (b) potassium chlorate, sulphur and phosphorus (c) sodium chloride, sugar and carbon (d) calcium carbonate and sulphur

Black gunpowder is roughly 75% potassium nitrate (saltpetre), 15% charcoal and 10% sulphur. Answer: (a).

Common mistakes

• Skipping the materials list because the school textbook did. It is named in the syllabus.
• Confusing look-alike names: baking soda and washing soda, quicklime and slaked lime, gypsum and plaster of Paris.
• Using "reversible" as the test for a physical change. The real test is whether a new substance forms.
• Memorising formulas without valency. If you know Al is 3 and SO₄ is 2, you can rebuild Al₂(SO₄)₃ under pressure.
• Guessing wildly on statement questions. With one-third negative marking, guess only after eliminating at least two options.

Practice set

1. The pH of pure water at 25 °C is: (a) 0 (b) 7 (c) 10 (d) 14
2. Bleaching powder is: (a) CaCO₃ (b) CaSO₄ (c) CaO (d) CaOCl₂
3. Which of these is a mixture? (a) water (b) carbon dioxide (c) air (d) common salt
4. Isotopes of an element have the same: (a) atomic number (b) number of neutrons (c) mass number (d) mass
5. Which metal is liquid at room temperature? (a) sodium (b) aluminium (c) zinc (d) mercury
6. Rusting of iron is an example of: (a) reduction (b) oxidation (c) sublimation (d) neutralisation
7. The main constituent of natural gas is: (a) methane (b) butane (c) ethane (d) propane
8. Cement is made mainly by strongly heating: (a) sand and soda ash (b) limestone and clay (c) gypsum and sand (d) bauxite and coke

Answers:

1. (b). Neutral water has equal H⁺ and OH⁻ concentrations.
2. (d). Made by passing chlorine over slaked lime.
3. (c). Its composition varies, and its gases can be separated physically.
4. (a). They differ in neutrons, so their mass numbers differ.
5. (d). Gallium melts at about 30 °C, just above room temperature.
6. (b). Iron combines with oxygen in the presence of water.
7. (a). CNG is compressed natural gas, mostly methane.
8. (b). A little gypsum is then added to slow down setting.

What to do next

• Copy the chemistry lines of the current notification onto the first page of your chemistry notebook.
• Follow the six-week table in order, starting with matter and changes.
• Build one page for the materials list (soap, glass, ink, paper, cement, paints, matches, gunpowder) in week 6.
• Use the chemistry revision sheet for the final pass before the exam.