Chemical Reactions Class 10: NCERT Exercise Solutions
An answer companion to the 20 NCERT Chemical Reactions and Equations exercise questions, with balancing steps and concise explanations.
About 4 min readReviewed by Codex (AI content review)Syllabus NCERT 2026–27 reprint (selected topics)Updated 4/9/2026
Use the NCERT 2026–27 reprint, chapter 1, pages 14–16, for the original questions. This companion contains Udayy’s answers and working rather than a reproduction of the exercise. For experiments mentioned by the textbook, follow your school’s laboratory supervision and instructions.
Open the official chapter exercise
Questions 1–4: identify and explain
- 1. Option (i): statements (a) and (b) are incorrect. Lead oxide, rather than the product lead, is reduced; carbon is oxidised to carbon dioxide.
- 2. Option (d): displacement. Aluminium removes oxygen from iron(III) oxide; the reaction is also redox.
- 3. Option (a): hydrogen and iron(II) chloride form. Fe + 2HCl → FeCl₂ + H₂.
- 4. A balanced equation has equal numbers of each element’s atoms on both sides, consistent with conservation of mass.
Questions 5–8: balanced equations
| Part | Answer |
|---|---|
| 5(a) | N₂ + 3H₂ → 2NH₃ |
| 5(b) | 2H₂S + 3O₂ → 2H₂O + 2SO₂ |
| 5(c) | 3BaCl₂ + Al₂(SO₄)₃ → 2AlCl₃ + 3BaSO₄ |
| 5(d) | 2K + 2H₂O → 2KOH + H₂ |
| 6(a) | 2HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + 2H₂O |
| 6(b) | 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O |
| 6(c) | NaCl + AgNO₃ → AgCl + NaNO₃ |
| 6(d) | BaCl₂ + H₂SO₄ → BaSO₄ + 2HCl |
| 7(a) | Ca(OH)₂ + CO₂ → CaCO₃ + H₂O |
| 7(b) | Zn + 2AgNO₃ → Zn(NO₃)₂ + 2Ag |
| 7(c) | 2Al + 3CuCl₂ → 2AlCl₃ + 3Cu |
| 7(d) | BaCl₂ + K₂SO₄ → BaSO₄ + 2KCl |
| 8(a) | 2KBr + BaI₂ → 2KI + BaBr₂; formal double displacement |
| 8(b) | ZnCO₃ → ZnO + CO₂; decomposition on heating |
| 8(c) | H₂ + Cl₂ → 2HCl; combination |
| 8(d) | Mg + 2HCl → MgCl₂ + H₂; displacement |
For 8(a), the textbook labels BaBr₂ as a solid. Barium bromide is soluble in water, so do not use this formal ion-exchange equation as an example of precipitation in aqueous solution. Use AgCl or BaSO₄ for a precipitation example.
How to balance 7(c)
- 1Start with Al + CuCl₂ → AlCl₃ + Cu. Chlorine appears in groups of 2 and 3; use their LCM, 6.
- 2Put 3 before CuCl₂ and 2 before AlCl₃. Then balance Al with 2 and Cu with 3.
- 3Check Al: 2 each side; Cu: 3 each side; Cl: 6 each side.
Questions 9–13: energy and reaction types
- 9. Exothermic reactions release energy to the surroundings, as in methane combustion. Endothermic reactions absorb energy, as in thermal decomposition of calcium carbonate.
- 10. Cellular respiration releases usable energy as glucose is broken down; that energy supports cell processes.
- 11. Combination builds one product from multiple reactants; decomposition splits one reactant. Examples: CaO + H₂O → Ca(OH)₂; CaCO₃ → CaO + CO₂ on heating.
- 12. Heat: CaCO₃ → CaO + CO₂. Light: 2AgCl → 2Ag + Cl₂. Electricity: 2H₂O → 2H₂ + O₂. The energy conditions are essential.
- 13. Displacement replaces an element: Zn + CuSO₄ → ZnSO₄ + Cu. Double displacement exchanges ions: BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl.
Questions 14–20: apply the ideas
- 14. Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag.
- 15. Precipitation produces an insoluble solid from solution; aqueous BaCl₂ + Na₂SO₄ forms solid BaSO₄, and aqueous AgNO₃ + NaCl forms solid AgCl.
- 16. Oxygen gain is oxidation: 2Cu + O₂ → 2CuO and 2Mg + O₂ → 2MgO. Oxygen loss is reduction: CuO + H₂ → Cu + H₂O and ZnO + C → Zn + CO.
- 17. X is copper and the black product is copper(II) oxide, CuO.
- 18. Paint provides a barrier against air and moisture, slowing iron corrosion.
- 19. Nitrogen displaces oxygen in the packaging, helping slow oxidation of fats and oils.
- 20. Corrosion: iron rusting in moist air. Rancidity: oxidation causing unpleasant changes in fats or oils, such as stale-smelling oil.
Sources
- Open the official chapter exercise — NCERT
- PubChem: Barium bromide, solubility reference — Source publisher