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Class 10 Science – Acids, Bases

14 October 2026
Class 10 Acids Bases and Salts Notes 90x80

Class 10 Science Acids, Bases and

14 October 2026
Class 10 Science Important Questions 1 90x80

Important Questions of Chemical Reactions and

14 October 2026
Class 10 Chemical Reactions Cover 90x80

Class 10 Science Chemical Reactions and

14 October 2026

Important Questions of Chemical Reactions and Equations Class 10 CBSE

Class 10 Science Important Questions
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Prepare smartly for your Class 10 Science board examination! Practise these important questions from NCERT Chapter 1, Chemical Reactions and Equations. Revise chemical equations, reaction types, oxidation and reduction, corrosion and rancidity. Attempt each question before opening its answer.
How to use this worksheet: First solve the questions independently. Then open “Show Answer” to check your understanding. For equation-based questions, practise writing the complete balanced equation with state symbols wherever required.
CBSE CLASS 10 SCIENCE • 2026–27

Important Questions
Chemical Reactions and Equations

Chapter 1 | NCERT-Based Board Exam Preparation

MCQs Assertion–Reason Balanced Equations 3 & 5 Mark Questions HOTS & Revision

Section A: Multiple-Choice Questions Objective questions for quick practice • 1 mark each

1 mark

Q1. Which observation indicates that a chemical reaction may have taken place?

  1. Change in colour
  2. Evolution of a gas
  3. Change in temperature
  4. All of the above
Show Answer
Correct option: (d) All of the above. A change in state, colour, temperature or evolution of gas may indicate a chemical reaction.
1 mark

Q2. Why should a magnesium ribbon be cleaned before burning in air?

  1. To remove the oxide layer
  2. To increase its mass
  3. To change its chemical formula
  4. To make it a liquid
Show Answer
Correct option: (a) To remove the oxide layer. The layer of magnesium oxide is removed by rubbing the ribbon with sandpaper.
1 mark

Q3. Which of the following is a combination reaction?

  1. CaCO₃ → CaO + CO₂
  2. 2Mg + O₂ → 2MgO
  3. Fe + CuSO₄ → FeSO₄ + Cu
  4. 2AgCl → 2Ag + Cl₂
Show Answer
Correct option: (b) 2Mg + O₂ → 2MgO. Two reactants combine to form a single product.
1 mark

Q4. Which reaction is an example of thermal decomposition?

  1. CaO + H₂O → Ca(OH)₂
  2. Fe + CuSO₄ → FeSO₄ + Cu
  3. CaCO₃ → CaO + CO₂ on heating
  4. Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
Show Answer
Correct option: (c). Calcium carbonate decomposes into calcium oxide and carbon dioxide when heated.
1 mark

Q5. When an iron nail is dipped in copper sulphate solution, the brown coating on the nail is due to the formation of:

  1. Iron sulphate
  2. Copper
  3. Iron oxide
  4. Copper oxide
Show Answer
Correct option: (b) Copper. Iron displaces copper from copper sulphate solution, depositing copper on the nail.
1 mark

Q6. Which gas is released when zinc reacts with dilute hydrochloric acid?

  1. Oxygen
  2. Hydrogen
  3. Nitrogen
  4. Chlorine
Show Answer
Correct option: (b) Hydrogen. Zn + 2HCl → ZnCl₂ + H₂
1 mark

Q7. The white precipitate formed when sodium sulphate reacts with barium chloride is:

  1. Sodium chloride
  2. Barium sulphate
  3. Barium oxide
  4. Sodium oxide
Show Answer
Correct option: (b) Barium sulphate (BaSO₄).
1 mark

Q8. A substance that gains oxygen during a chemical reaction is said to be:

  1. Reduced
  2. Oxidised
  3. Neutralised
  4. Precipitated
Show Answer
Correct option: (b) Oxidised.
1 mark

Q9. Which substance is used to prevent oxidation of fats and oils in food?

  1. Antioxidants
  2. Water
  3. Rust
  4. Iron filings
Show Answer
Correct option: (a) Antioxidants. Airtight storage and flushing food packets with nitrogen can also help slow oxidation.
1 mark

Q10. Which of the following is a photochemical decomposition reaction?

  1. 2AgCl → 2Ag + Cl₂ in sunlight
  2. CaO + H₂O → Ca(OH)₂
  3. Fe + CuSO₄ → FeSO₄ + Cu
  4. 2H₂ + O₂ → 2H₂O
Show Answer
Correct option: (a). Silver chloride decomposes into silver and chlorine in the presence of sunlight.

Section B: Very Short Answer Questions 2-mark questions • Definitions, reasons and observations

Q11. What is a chemical reaction? Mention any two observations that indicate a chemical reaction.

Show Answer
A chemical reaction is a process in which one or more substances change to form new substances. Any two indicators are change in colour, change in state, evolution of a gas or change in temperature.

Q12. Define a balanced chemical equation. Why must a chemical equation be balanced?

Show Answer
A balanced chemical equation has the same number of atoms of each element on both sides. It must be balanced to obey the law of conservation of mass.

Q13. What is a skeletal chemical equation? Give one example.

Show Answer
A skeletal equation is an unbalanced chemical equation. Example: Mg + O₂ → MgO

Q14. What is an exothermic reaction? Give one example from everyday life.

Show Answer
An exothermic reaction releases heat. Respiration is an example.
See also  Class 10 Science Acids, Bases and Salts Notes | Quick Revision for Exams
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

Q15. What is an endothermic reaction? Name the forms of energy that can cause decomposition reactions.

Show Answer
An endothermic reaction absorbs energy. Decomposition may be brought about by heat, light or electricity.

Q16. Define corrosion and rancidity.

Show Answer
Corrosion: The deterioration of a metal due to its reaction with substances in its surroundings.
Rancidity: The oxidation of fats and oils that changes the smell and taste of food.

Q17. Why do we paint iron articles?

Show Answer
Paint forms a protective coating that prevents iron from coming into contact with air and moisture, helping to prevent rusting.

Q18. Why are packets of chips often flushed with nitrogen gas?

Show Answer
Nitrogen reduces contact with oxygen and helps prevent oxidation of fats and oils, delaying rancidity.

Section C: Balance the Chemical Equations High-priority practice • Write coefficients carefully

Q19. Balance the following equation:

H₂ + Cl₂ → HCl
Show Answer
H₂ + Cl₂ → 2HCl

Q20. Balance the reaction between sodium and water.

Na + H₂O → NaOH + H₂
Show Answer
2Na + 2H₂O → 2NaOH + H₂

Q21. Balance the equation for the reaction between barium chloride and aluminium sulphate.

BaCl₂ + Al₂(SO₄)₃ → BaSO₄ + AlCl₃
Show Answer
3BaCl₂ + Al₂(SO₄)₃ → 3BaSO₄ + 2AlCl₃

Q22. Balance the equation:

Fe + H₂O → Fe₃O₄ + H₂
Show Answer
3Fe + 4H₂O → Fe₃O₄ + 4H₂

Q23. Balance the thermal decomposition of lead nitrate.

Pb(NO₃)₂ → PbO + NO₂ + O₂
Show Answer
2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂

Q24. Balance the reaction between sodium hydroxide and sulphuric acid.

NaOH + H₂SO₄ → Na₂SO₄ + H₂O
Show Answer
2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O

Q25. Write the balanced equation with state symbols for the reaction between aqueous barium chloride and aqueous sodium sulphate.

Show Answer
BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)Barium sulphate forms an insoluble white precipitate.

Q26. Write the balanced equation with state symbols for sodium hydroxide solution reacting with hydrochloric acid solution.

Show Answer
NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)

Q27. Write the balanced equation for the reaction of zinc with dilute hydrochloric acid. Include state symbols.

Show Answer
Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

Section D: Identify the Type of Reaction Practise identifying reactions from their equations

Q28. Identify the reaction type:

CaO + H₂O → Ca(OH)₂ + heat
Show Answer
Combination reaction and exothermic reaction. Two reactants form one product, and heat is released.

Q29. Identify the reaction type:

2AgCl(s) → 2Ag(s) + Cl₂(g) (in sunlight)
Show Answer
Photochemical decomposition reaction. Light supplies the energy required to break down silver chloride.

Q30. Identify the reaction type:

Fe + CuSO₄ → FeSO₄ + Cu
Show Answer
Displacement reaction. Iron displaces copper from copper sulphate solution.

Q31. Identify the reaction type:

Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
Show Answer
Double displacement reaction and precipitation reaction. The ions exchange partners and insoluble barium sulphate forms.

Q32. Identify the reaction type:

2H₂ + O₂ → 2H₂O
Show Answer
Combination reaction because two reactants combine to form a single product.

Q33. Identify the reaction type and explain the energy change:

CaCO₃(s) → CaO(s) + CO₂(g) (on heating)
Show Answer
Thermal decomposition reaction. Calcium carbonate breaks down into calcium oxide and carbon dioxide when heat is supplied.

Section E: Short Answer Questions 3-mark questions • Explain with equations wherever appropriate

Q34. Explain combination and decomposition reactions with one balanced chemical equation for each.

Show Answer

Combination: Two or more substances combine to form one product.

2Mg + O₂ → 2MgO

Decomposition: One substance breaks down into two or more simpler substances.

CaCO₃ → CaO + CO₂ (on heating)

Q35. Differentiate between displacement and double displacement reactions. Give one equation for each.

Show Answer

Displacement: A more reactive element displaces a less reactive element from its compound.

Fe + CuSO₄ → FeSO₄ + Cu

Double displacement: Two compounds exchange ions to form new compounds.

Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl

Q36. Explain oxidation and reduction in terms of gain and loss of oxygen. Give an example of a redox reaction.

Show Answer

Oxidation: Gain of oxygen or loss of hydrogen.

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Reduction: Loss of oxygen or gain of hydrogen.

CuO + H₂ → Cu + H₂O (on heating)

CuO loses oxygen and is reduced to copper. Hydrogen gains oxygen and is oxidised to water. Both occur simultaneously, so this is a redox reaction.

Q37. What happens when copper powder is heated in air? What happens when hydrogen is passed over the heated product?

Show Answer

Copper powder develops a black coating of copper(II) oxide.

2Cu + O₂ → 2CuO

When hydrogen is passed over heated copper oxide, the black coating turns brown as copper is formed.

CuO + H₂ → Cu + H₂O

Q38. Explain why respiration is considered an exothermic process.

Show Answer
During respiration, glucose reacts with oxygen to produce carbon dioxide and water, releasing energy needed by the body.

Q39. What is a precipitation reaction? Explain with an example.

Show Answer
A precipitation reaction forms an insoluble solid called a precipitate when suitable solutions react. For example: Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq) The white solid is barium sulphate.

Q40. Explain why decomposition reactions are considered the opposite of combination reactions.

Show Answer
In a combination reaction, two or more reactants form one product. In a decomposition reaction, one reactant breaks down into two or more products. Combination: 2H₂ + O₂ → 2H₂O Decomposition: CaCO₃ → CaO + CO₂ (on heating)

Section F: Long Answer Questions 5-mark practice • Board-style explanations and applications

Q41. Explain the different types of chemical reactions with one balanced equation for each: combination, decomposition, displacement and double displacement.

Show Answer

1. Combination: Two or more reactants form one product.

2Mg + O₂ → 2MgO

2. Decomposition: One reactant breaks down into simpler products.

CaCO₃ → CaO + CO₂ (on heating)

3. Displacement: A more reactive element displaces another element from its compound.

Fe + CuSO₄ → FeSO₄ + Cu

4. Double displacement: Two compounds exchange ions.

Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl

Q42. Describe three types of decomposition reactions with balanced chemical equations. Explain the energy source in each case.

Show Answer

Thermal decomposition — heat:

CaCO₃(s) → CaO(s) + CO₂(g)

Photochemical decomposition — sunlight:

2AgCl(s) → 2Ag(s) + Cl₂(g)

Electrolytic decomposition — electricity:

2H₂O(l) → 2H₂(g) + O₂(g)

Each reaction requires energy to break down the reactant.

Q43. Explain the reaction between iron and copper sulphate solution. State the observations, write the balanced equation and identify the reaction type.

Show Answer

Iron nails are placed in blue copper sulphate solution. The blue colour fades as iron sulphate forms, and a brown coating of copper appears on the nail.

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

Iron displaces copper because iron is more reactive than copper. It is a displacement reaction.

Q44. Define oxidation and reduction. Explain how both processes occur simultaneously in the reaction between copper(II) oxide and hydrogen.

Show Answer

Oxidation involves gain of oxygen or loss of hydrogen. Reduction involves loss of oxygen or gain of hydrogen.

CuO + H₂ → Cu + H₂O (on heating)

Copper(II) oxide loses oxygen and is reduced to copper. Hydrogen gains oxygen and is oxidised to water. Since oxidation and reduction occur together, the reaction is a redox reaction.

Q45. What are corrosion and rancidity? Explain their effects and describe methods to prevent them.

Show Answer

Corrosion: Deterioration of metals due to reactions with substances in their surroundings. It damages iron railings, bridges, ships and other metal objects. Painting iron articles helps prevent contact with air and moisture.

Rancidity: Oxidation of fats and oils that changes the smell and taste of food. It can be slowed by adding antioxidants, storing food in airtight containers and flushing packets with nitrogen.

Section G: Assertion–Reason Questions Choose the correct option for each question

Options:
(a) Both Assertion and Reason are true, and Reason correctly explains Assertion.
(b) Both are true, but Reason does not correctly explain Assertion.
(c) Assertion is true, but Reason is false.
(d) Assertion is false, but Reason is true.

Q46. Assertion: A chemical equation must be balanced.
Reason: Atoms are conserved in a chemical reaction.

Show Answer
Correct option: (a). Conservation of atoms requires equal numbers of each type of atom on both sides.

Q47. Assertion: Respiration is an exothermic process.
Reason: Energy is released when glucose reacts with oxygen during respiration.

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Show Answer
Correct option: (a). The release of energy explains why respiration is exothermic.

Q48. Assertion: Silver chloride turns grey when exposed to sunlight.
Reason: Silver chloride decomposes into silver and chlorine in sunlight.

Show Answer
Correct option: (a). The formation of grey silver causes the colour change.

Q49. Assertion: Iron displaces copper from copper sulphate solution.
Reason: Copper is more reactive than iron.

Show Answer
Correct option: (c). The assertion is true, but the reason is false. Iron is more reactive than copper.

Q50. Assertion: Rancidity can be delayed by storing food in airtight containers.
Reason: Airtight storage reduces contact with oxygen.

Show Answer
Correct option: (a). Reducing exposure to oxygen slows oxidation of fats and oils.

Section H: HOTS and Application-Based Questions Develop conceptual clarity for board examinations

Q51. A shiny brown metal powder turns black when heated in air. Identify the metal and the black compound formed. Write the chemical equation.

Show Answer
The metal is copper and the black compound is copper(II) oxide. 2Cu + O₂ → 2CuO

Q52. A student mixes aqueous solutions of lead(II) nitrate and potassium iodide. A yellow precipitate forms. What is the precipitate? Write the balanced equation and identify the reaction type.

Show Answer
The yellow precipitate is lead(II) iodide. Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s) + 2KNO₃(aq) It is a double displacement and precipitation reaction.

Q53. Why does the blue colour of copper sulphate solution fade when an iron nail is placed in it? What would happen if a copper strip were placed in iron sulphate solution?

Show Answer
Iron displaces copper from copper sulphate, forming iron sulphate and copper. Copper is less reactive than iron, so a copper strip cannot displace iron from iron sulphate solution under these conditions.

Q54. A student heats ferrous sulphate crystals. The green crystals change colour and gases with a characteristic burning sulphur smell are released. Identify the products and write the balanced equation.

Show Answer
Ferrous sulphate decomposes to ferric oxide, sulphur dioxide and sulphur trioxide. 2FeSO₄(s) → Fe₂O₃(s) + SO₂(g) + SO₃(g) (on heating)

Q55. A food packet is exposed to air for a long time and develops an unpleasant smell and taste. Name the process responsible and suggest two preventive measures.

Show Answer
The process is rancidity. It can be slowed by storing food in airtight containers, adding antioxidants, or flushing suitable food packets with nitrogen.

Quick Revision: Chemical Reactions and Equations

  • Signs of a reaction: Change in state, colour or temperature; evolution of gas.
  • Balanced equation: Equal number of atoms of every element on both sides.
  • Combination: Two or more reactants form one product.
  • Decomposition: One reactant forms two or more products.
  • Displacement: A more reactive element replaces a less reactive element.
  • Double displacement: Exchange of ions between two compounds.
  • Precipitation: Formation of an insoluble solid.
  • Exothermic: Energy is released.
  • Endothermic: Energy is absorbed.
  • Oxidation: Gain of oxygen or loss of hydrogen.
  • Reduction: Loss of oxygen or gain of hydrogen.
  • Corrosion: Deterioration of metals due to their surroundings.
  • Rancidity: Oxidation of fats and oils that changes food's smell and taste.

Must-Remember Equations

2Mg + O₂ → 2MgO
CaO + H₂O → Ca(OH)₂ + heat
CaCO₃ → CaO + CO₂ (on heating)
Fe + CuSO₄ → FeSO₄ + Cu
Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
CuO + H₂ → Cu + H₂O (on heating)
2AgCl → 2Ag + Cl₂ (in sunlight)

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