Science is one of the most scoring subjects in the CBSE Class 10 Board Examination, provided students understand the concepts thoroughly and practice regularly. At Dhingra Classes Nashik, we believe that solving Previous Year Questions (PYQs), Multiple Choice Questions (MCQs), Short Answer Questions, and Long Answer Questions is the key to mastering Science and scoring 95+ marks.

In this article, we provide a comprehensive set of 25 solved PYQs, 25 solved MCQs, 25 solved short Q&A, 25 solved long Q&A, and 4 solved activities based on Lesson 1: Chemical Reactions and Equations from the CBSE Class 10 Science syllabus. This guide is designed to help students revise effectively and build confidence for the 2026 board examinations.

CBSE Class 10 Science – Lesson 1: Chemical Reactions and Equations

Key Concepts Covered:

• Chemical reactions and their characteristics

• Types of chemical reactions (Combination, Decomposition, Displacement, Double Displacement, Redox)

• Balancing chemical equations

• Oxidation and Reduction

• Corrosion and Rancidity

📌 Section A – 25 Solved MCQs (Multiple Choice Questions)

1. Which of the following is a chemical change?
(a) Melting of ice
(b) Dissolving sugar in water
(c) Rusting of iron
(d) Boiling of water

✅ Answer: (c) Rusting of iron

2. The chemical formula of quicklime is:
(a) CaCO₃
(b) CaO
(c) Ca(OH)₂
(d) CaCl₂

✅ Answer: (b) CaO

3. Which type of reaction is: 2H₂ + O₂ → 2H₂O?
(a) Decomposition
(b) Displacement
(c) Combination
(d) Double Displacement

✅ Answer: (c) Combination

4. The reaction between iron and copper sulphate solution is an example of:
(a) Combination reaction
(b) Decomposition reaction
(c) Displacement reaction
(d) Double displacement reaction

✅ Answer: (c) Displacement reaction

5. Which of the following is a redox reaction?
(a) NaCl + AgNO₃ → AgCl + NaNO₃
(b) 2Mg + O₂ → 2MgO
(c) Zn + CuSO₄ → ZnSO₄ + Cu
(d) Both (b) and (c)

✅ Answer: (d) Both (b) and (c)

6. The colour of ferrous sulphate solution is:
(a) Blue
(b) Green
(c) Yellow
(d) Colourless

✅ Answer: (b) Green

7. Which gas is evolved when zinc reacts with dilute hydrochloric acid?
(a) Oxygen
(b) Hydrogen
(c) Chlorine
(d) Nitrogen

✅ Answer: (b) Hydrogen

8. The reaction: 2AgCl → 2Ag + Cl₂ is an example of:
(a) Combination reaction
(b) Decomposition reaction
(c) Displacement reaction
(d) Double displacement reaction

✅ Answer: (b) Decomposition reaction

9. The substance that gets oxidized in the reaction: Zn + CuSO₄ → ZnSO₄ + Cu is:
(a) CuSO₄
(b) Zn
(c) Cu
(d) ZnSO₄

✅ Answer: (b) Zn

10. Which of the following is NOT a type of chemical reaction?
(a) Combination
(b) Decomposition
(c) Sublimation
(d) Displacement

✅ Answer: (c) Sublimation

11. The reaction between an acid and a base is called:
(a) Redox reaction
(b) Neutralization reaction
(c) Displacement reaction
(d) Decomposition reaction

✅ Answer: (b) Neutralization reaction

12. When magnesium ribbon burns in air, the product formed is:
(a) MgO
(b) Mg(OH)₂
(c) MgCl₂
(d) MgCO₃

✅ Answer: (a) MgO

13. The reaction: 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂ is an example of:
(a) Combination reaction
(b) Decomposition reaction
(c) Displacement reaction
(d) Double displacement reaction

✅ Answer: (b) Decomposition reaction

14. Which of the following is an endothermic reaction?
(a) Burning of coal
(b) Respiration
(c) Photosynthesis
(d) Neutralization

✅ Answer: (c) Photosynthesis

15. The reaction: NaCl + AgNO₃ → AgCl + NaNO₃ is an example of:
(a) Combination reaction
(b) Decomposition reaction
(c) Displacement reaction
(d) Double displacement reaction

✅ Answer: (d) Double displacement reaction

16. Which of the following is a physical change?
(a) Rusting of iron
(b) Burning of candle
(c) Melting of ice
(d) Digestion of food

✅ Answer: (c) Melting of ice

17. The chemical equation: 2H₂ + O₂ → 2H₂O is balanced because:
(a) Atoms are equal on both sides
(b) Molecules are equal on both sides
(c) Mass is conserved
(d) Both (a) and (c)

✅ Answer: (d) Both (a) and (c)

18. The process of gaining oxygen is called:
(a) Reduction
(b) Oxidation
(c) Corrosion
(d) Rancidity

✅ Answer: (b) Oxidation

19. Which of the following is a reducing agent?
(a) O₂
(b) H₂
(c) Cl₂
(d) F₂

✅ Answer: (b) H₂

20. The reaction: Fe + CuSO₄ → FeSO₄ + Cu is an example of:
(a) Combination reaction
(b) Decomposition reaction
(c) Displacement reaction
(d) Double displacement reaction

✅ Answer: (c) Displacement reaction

21. Which of the following is NOT a redox reaction?
(a) 2Mg + O₂ → 2MgO
(b) Zn + CuSO₄ → ZnSO₄ + Cu
(c) NaCl + AgNO₃ → AgCl + NaNO₃
(d) 2H₂ + O₂ → 2H₂O

✅ Answer: (c) NaCl + AgNO₃ → AgCl + NaNO₃

22. The chemical formula of rust is:
(a) FeO
(b) Fe₂O₃
(c) Fe₃O₄
(d) Fe₂O₃·xH₂O

✅ Answer: (d) Fe₂O₃·xH₂O

23. Which of the following is a double displacement reaction?
(a) 2H₂ + O₂ → 2H₂O
(b) NaOH + HCl → NaCl + H₂O
(c) Zn + CuSO₄ → ZnSO₄ + Cu
(d) 2Mg + O₂ → 2MgO

✅ Answer: (b) NaOH + HCl → NaCl + H₂O

24. The reaction in which a single compound breaks down into simpler substances is called:
(a) Combination reaction
(b) Decomposition reaction
(c) Displacement reaction
(d) Double displacement reaction

✅ Answer: (b) Decomposition reaction

25. The product formed when calcium carbonate is heated is:
(a) CaO and CO₂
(b) Ca(OH)₂ and CO₂
(c) CaCl₂ and CO₂
(d) CaO and H₂O

✅ Answer: (a) CaO and CO₂

📌 Section B – 25 Solved Short Answer Questions (2–3 Marks)

Q1. What is a chemical reaction? Give one example.

Answer: A chemical reaction is a process in which one or more substances (reactants) are converted into one or more new substances (products) with different chemical properties.

Example: Rusting of iron – Iron reacts with oxygen and moisture to form iron oxide (rust).
Equation: 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃

Q2. Balance the following chemical equation: Fe + H₂O → Fe₃O₄ + H₂

Answer:
Unbalanced: Fe + H₂O → Fe₃O₄ + H₂
Balanced: 3Fe + 4H₂O → Fe₃O₄ + 4H₂

Q3. What is a decomposition reaction? Give an example.

Answer: A decomposition reaction is a reaction in which a single compound breaks down into two or more simpler substances.

Example: Heating of calcium carbonate (CaCO₃) produces calcium oxide (CaO) and carbon dioxide (CO₂).
Equation: CaCO₃ → CaO + CO₂

Q4. Why is respiration considered an exothermic reaction?

Answer: Respiration is considered an exothermic reaction because it releases energy in the form of heat. During respiration, glucose reacts with oxygen to produce carbon dioxide, water, and energy.

Equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy

Q5. Define oxidation and reduction with examples.

Answer:
Oxidation: Addition of oxygen or removal of hydrogen.
Example: 2Mg + O₂ → 2MgO (Magnesium is oxidized)

Reduction: Addition of hydrogen or removal of oxygen.
Example: CuO + H₂ → Cu + H₂O (CuO is reduced to Cu)

Q6. What is a displacement reaction? Give an example.

Answer: A displacement reaction is a reaction in which a more reactive element displaces a less reactive element from its compound.

Example: Zn + CuSO₄ → ZnSO₄ + Cu (Zinc displaces copper from copper sulphate)

Q7. What is a double displacement reaction? Give an example.

Answer: A double displacement reaction is a reaction in which ions are exchanged between two reactants.

Example: NaCl + AgNO₃ → AgCl + NaNO₃ (Sodium chloride reacts with silver nitrate to form silver chloride and sodium nitrate)

Q8. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

Answer: When an iron nail is dipped in copper sulphate solution, iron displaces copper from copper sulphate, forming ferrous sulphate and copper. The blue colour of the solution changes to green due to the formation of ferrous sulphate.

Equation: Fe + CuSO₄ → FeSO₄ + Cu

Q9. What is corrosion? Give an example.

Answer: Corrosion is the slow deterioration of metals due to chemical reactions with their environment. Rusting of iron is a common example of corrosion.

Equation: 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃

Q10. What is rancidity? How can it be prevented?

Answer: Rancidity is the oxidation of fats and oils in food, leading to an unpleasant smell and taste.

Prevention Methods:

1. Adding antioxidants

2. Storing in air-tight containers

3. Refrigeration

4. Nitrogen packaging

Q11. Balance the equation: MnO₂ + HCl → MnCl₂ + Cl₂ + H₂O

Answer:
Unbalanced: MnO₂ + HCl → MnCl₂ + Cl₂ + H₂O
Balanced: MnO₂ + 4HCl → MnCl₂ + Cl₂ + 2H₂O

Q12. What is a redox reaction? Give an example.

Answer: A redox reaction is a reaction in which both oxidation and reduction occur simultaneously.

Example: Zn + CuSO₄ → ZnSO₄ + Cu (Zn is oxidized, Cu is reduced)

Q13. Why is the reaction between NaOH and HCl called a neutralization reaction?

Answer: The reaction between NaOH (a base) and HCl (an acid) produces salt (NaCl) and water (H₂O). Since acid and base neutralize each other, it is called a neutralization reaction.

Equation: NaOH + HCl → NaCl + H₂O

Q14. What is the law of conservation of mass? How is it applied in chemical reactions?

Answer: The law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction. In a chemical reaction, the total mass of reactants is equal to the total mass of products. This is achieved by balancing chemical equations.

Q15. What is an exothermic reaction? Give an example.

Answer: An exothermic reaction is a reaction that releases energy in the form of heat.

Example: Burning of coal: C + O₂ → CO₂ + Heat

Q16. What is an endothermic reaction? Give an example.

Answer: An endothermic reaction is a reaction that absorbs energy in the form of heat.

Example: Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Q17. What is the difference between a physical change and a chemical change?

Q18. Why is respiration considered a chemical reaction?

Answer: Respiration is considered a chemical reaction because glucose and oxygen react to form carbon dioxide, water, and energy. New substances are formed, so it is a chemical change.

Equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy

Q19. What is the role of a catalyst in a chemical reaction?

Answer: A catalyst is a substance that speeds up a chemical reaction without being consumed in the process. It lowers the activation energy required for the reaction to occur.

Q20. What is the difference between a combination reaction and a decomposition reaction?

Q21. What is the difference between a displacement reaction and a double displacement reaction?

Q22. Why is the reaction between copper oxide and hydrogen considered a redox reaction?

Answer: In the reaction CuO + H₂ → Cu + H₂O:

• CuO loses oxygen → reduction (Cu is reduced)

• H₂ gains oxygen → oxidation (H₂ is oxidized)

Since both oxidation and reduction occur, it is a redox reaction.

Q23. What is the chemical equation for the reaction between zinc and dilute sulphuric acid?

Answer: Zn + H₂SO₄ → ZnSO₄ + H₂

Q24. Why is sodium kept in kerosene oil?

Answer: Sodium is a highly reactive metal that reacts vigorously with oxygen and moisture in the air. To prevent this reaction, sodium is kept in kerosene oil.

Q25. What is the significance of balancing a chemical equation?

Answer: Balancing a chemical equation ensures that the law of conservation of mass is followed. It means the number of atoms of each element is the same on both sides of the equation.

📌 Section C – 25 Solved Long Answer Questions (5 Marks)

Q1. Explain the different types of chemical reactions with one example each.

Answer: Chemical reactions are classified into the following types:

1. Combination Reaction: Two or more reactants combine to form a single product.
Example: 2H₂ + O₂ → 2H₂O

2. Decomposition Reaction: A single compound breaks down into two or more simpler substances.
Example: CaCO₃ → CaO + CO₂

3. Displacement Reaction: A more reactive element displaces a less reactive element from its compound.
Example: Zn + CuSO₄ → ZnSO₄ + Cu

4. Double Displacement Reaction: Exchange of ions between two reactants occurs.
Example: NaCl + AgNO₃ → AgCl + NaNO₃

5. Redox Reaction: Both oxidation and reduction occur simultaneously.
Example: Zn + CuSO₄ → ZnSO₄ + Cu (Zn is oxidized, Cu is reduced)

Q2. Explain the process of balancing a chemical equation with an example.

Answer: Balancing a chemical equation ensures that the number of atoms of each element is the same on both sides of the equation, following the law of conservation of mass.

Steps:

1. Write the unbalanced equation.

2. Count the number of atoms of each element.

3. Use coefficients to balance the atoms.

4. Double-check that all atoms are balanced.

Example: Fe + H₂O → Fe₃O₄ + H₂

Balanced Equation: 3Fe + 4H₂O → Fe₃O₄ + 4H₂

Q3. What is corrosion? How can it be prevented?

Answer: Corrosion is the slow deterioration of metals due to chemical reactions with their environment. Rusting of iron is a common example of corrosion.

Prevention Methods:

1. Painting – Prevents moisture and oxygen contact.

2. Galvanization – Coating iron with zinc.

3. Oiling or Greasing – Protects metals from moisture.

4. Alloying – Mixing metals to improve resistance.

5. Cathodic Protection – Using sacrificial anodes.

Q4. What is rancidity? How can it be prevented?

Answer: Rancidity is the oxidation of fats and oils in food, leading to an unpleasant smell and taste.

Prevention Methods:

1. Adding Antioxidants – Prevent oxidation.

2. Storing in Air-tight Containers – Prevents oxygen exposure.

3. Refrigeration – Slows down oxidation.

4. Nitrogen Packaging – Replaces oxygen with nitrogen.

Q5. What is a redox reaction? Explain with an example.

Answer: A redox reaction is a reaction in which both oxidation and reduction occur simultaneously.

Example: In the reaction Zn + CuSO₄ → ZnSO₄ + Cu:

• Zn loses electrons → oxidation (Zn is oxidized to Zn²⁺)

• Cu²⁺ gains electrons → reduction (Cu²⁺ is reduced to Cu)

Equation: Zn + Cu²⁺ → Zn²⁺ + Cu

Q6. Write a balanced chemical equation for the reaction between potassium chloride and silver nitrate. Identify the type of reaction.

Answer:
Equation: KCl + AgNO₃ → KNO₃ + AgCl
Type: Double displacement reaction

Q7. Explain the difference between exothermic and endothermic reactions with examples.

Answer:
Exothermic Reaction: Releases energy in the form of heat.
Example: Burning of coal: C + O₂ → CO₂ + Heat

Endothermic Reaction: Absorbs energy in the form of heat.
Example: Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

Q8. What are the characteristics of a chemical reaction? Explain with examples.

Answer: The characteristics of a chemical reaction are:

1. Evolution of Gas: Example: Zn + H₂SO₄ → ZnSO₄ + H₂

2. Change in Colour: Example: Fe + CuSO₄ → FeSO₄ + Cu

3. Change in Temperature: Example: NaOH + HCl → NaCl + H₂O (exothermic)

4. Formation of Precipitate: Example: NaCl + AgNO₃ → AgCl + NaNO₃

5. Change in State: Example: 2H₂ + O₂ → 2H₂O

Q9. Balance the following chemical equations:

(a) Pb(NO₃)₂ → PbO + NO₂ + O₂
(b) Al + O₂ → Al₂O₃

Answer:
(a) 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂
(b) 4Al + 3O₂ → 2Al₂O₃

Q10. Why is photosynthesis considered an endothermic reaction?

Answer: Photosynthesis is considered an endothermic reaction because it absorbs sunlight energy to convert carbon dioxide and water into glucose and oxygen.

Equation: 6CO₂ + 6H₂O + Sunlight → C₆H₁₂O₆ + 6O₂

Q11. Write the balanced equation for the reaction between hydrochloric acid and sodium hydroxide. Identify the type of reaction.

Answer:
Equation: HCl + NaOH → NaCl + H₂O
Type: Neutralization reaction (Double displacement reaction)

Q12. What is a precipitate? Give an example.

Answer: A precipitate is an insoluble solid formed when two solutions react chemically.

Example: In the reaction NaCl + AgNO₃ → AgCl + NaNO₃, AgCl is the precipitate (white solid).

Q13. Explain the reaction between magnesium and oxygen. What type of reaction is it?

Answer: Magnesium reacts with oxygen to form magnesium oxide.

Equation: 2Mg + O₂ → 2MgO
Type: Combination reaction (also redox reaction)

Q14. Why is the reaction between iron and copper sulphate considered a displacement reaction?

Answer: Iron (more reactive) displaces copper (less reactive) from copper sulphate solution.

Equation: Fe + CuSO₄ → FeSO₄ + Cu

Q15. What is the chemical equation for the reaction between calcium carbonate and hydrochloric acid?

Answer: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂

Q16. Explain the reaction between zinc and dilute hydrochloric acid.

Answer: Zinc reacts with dilute hydrochloric acid to produce zinc chloride and hydrogen gas.

Equation: Zn + 2HCl → ZnCl₂ + H₂

Q17. What is the role of water in the rusting of iron?

Answer: Water acts as a medium for oxygen and iron to react. The rusting process requires both oxygen and water.

Equation: 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃

Q18. What are the products of the reaction between calcium oxide and water?

Answer: Calcium oxide reacts with water to form calcium hydroxide.

Equation: CaO + H₂O → Ca(OH)₂

Q19. What is the chemical equation for the reaction between sodium and water?

Answer: 2Na + 2H₂O → 2NaOH + H₂

Q20. Why is it necessary to balance a chemical equation?

Answer: It is necessary to balance a chemical equation to satisfy the law of conservation of mass. The number of atoms of each element must be equal on both sides.

Q21. Explain the reaction between silver nitrate and sodium chloride. Identify the type of reaction.

Answer:
Equation: AgNO₃ + NaCl → AgCl + NaNO₃
Type: Double displacement reaction

Q22. What is the chemical equation for the reaction between potassium chlorate and manganese dioxide?

Answer: 2KClO₃ → 2KCl + 3O₂ (MnO₂ is used as a catalyst)

Q23. Explain the reaction between lead nitrate and potassium iodide.

Answer: Lead nitrate reacts with potassium iodide to form lead iodide (yellow precipitate) and potassium nitrate.

Equation: Pb(NO₃)₂ + 2KI → PbI₂ + 2KNO₃

Q24. What is the difference between combustion and respiration?

Answer:
Combustion: Rapid oxidation producing heat and light.
Respiration: Slow oxidation in living cells producing energy.

Q25. Write a balanced chemical equation for the reaction between copper oxide and hydrogen. Identify the type of reaction.

Answer:
Equation: CuO + H₂ → Cu + H₂O
Type: Redox reaction (CuO is reduced, H₂ is oxidized)

📌 Section D – 4 Solved Activities

Activity 1: Burning of Magnesium Ribbon

Procedure: Take a magnesium ribbon and clean it. Hold it with tongs and burn it in the air. Observe the bright white flame and the white powder formed.

Observation: Magnesium burns with a dazzling white flame and forms a white powder (MgO).

Equation: 2Mg + O₂ → 2MgO
Type: Combination reaction

Activity 2: Reaction between Zinc and Dilute Hydrochloric Acid

Procedure: Take a few pieces of zinc in a test tube and add dilute hydrochloric acid. Observe the gas evolved.

Observation: Bubbles of hydrogen gas are evolved.

Equation: Zn + 2HCl → ZnCl₂ + H₂

Activity 3: Reaction between Iron Nail and Copper Sulphate Solution

Procedure: Take a copper sulphate solution in a beaker. Dip an iron nail into it and leave it for some time.

Observation: The blue colour of the solution changes to green, and a brown deposit appears on the nail.

Equation: Fe + CuSO₄ → FeSO₄ + Cu
Type: Displacement reaction

Activity 4: Reaction between Sodium Hydroxide and Hydrochloric Acid

Procedure: Take sodium hydroxide solution in a test tube and add hydrochloric acid. Observe the change in temperature.

Observation: The mixture becomes warm, indicating the release of heat.

Equation: NaOH + HCl → NaCl + H₂O
Type: Neutralization reaction (Double displacement reaction)

How Dhingra Classes Helps Students Master Science

At Dhingra Classes Nashik, we provide:

• Conceptual learning – Building strong fundamentals in Physics, Chemistry, and Biology.

• Regular practice – Worksheets, PYQs, MCQs, and mock tests.

• Doubt-clearing sessions – Instant clarification of queries.

• Personalized feedback – Identifying weak areas and providing targeted support.

Contact Dhingra Classes

• Phone: 98230 62106

• Email: dhingraclassesnsk@gmail.com

• Website: www.dhingraclassesnashik.com

• Address: Plot No 3, XQ3G+H3M Deacon Homes, 301C, opp. Metro Zone, near Guru Govind Sing, Samarth Nagar, Dnyaneshwar Nagar, Pathardi Phata, Nashik, Maharashtra 422009

Conclusion

Mastering Science Lesson 1: Chemical Reactions and Equations requires a thorough understanding of concepts and consistent practice of PYQs, MCQs, short Q&A, long Q&A, and activities. By solving these questions, students can build confidence and score high marks in the CBSE Class 10 board examinations.

At Dhingra Classes Nashik, we are committed to helping students achieve academic excellence through expert guidance and structured practice. Join us and embark on your journey to success!