🌟 Introduction

Chemical Reactions and Equations is the first and most fundamental chapter in the Class 10 CBSE Science syllabus. For students preparing for CBSE Board examinations, solving Previous Year Questions (PYQs) is the most effective way to understand the exam pattern, marking scheme, and frequently repeated themes. At Dhingra Classes Nashik, we have compiled the most important PYQs from this chapter, organized by marks weightage, to help Class 10 students score maximum marks.

This chapter covers Chemical Equations, Balancing Equations, Types of Chemical Reactions, Combination Reactions, Decomposition Reactions, Displacement Reactions, Double Displacement Reactions, Redox Reactions, Oxidation, Reduction, Corrosion, and Rancidity. These PYQs have been collected from CBSE Board exams across multiple years and are essential for effective board exam preparation.

📚 Why Solving PYQs Is Important for CBSE Class 10

Before diving into the questions, let us understand why Previous Year Questions are crucial for Class 10 CBSE students.

🎯 Benefits of Solving PYQs

• ✅ Understanding Exam Pattern: PYQs reveal how questions are framed

• 📝 Identifying Repeated Themes: Many questions repeat with slight variations

• 🧠 Better Answer Writing: PYQs help practice structured answers

• 🏆 Higher Scores: Familiarity with question types reduces exam stress

• 📊 Time Management: Practice helps allocate time per question correctly

• ⚗️ Equation Practice: Many PYQs require writing and balancing equations

📖 1 Mark Questions (Very Short Answer Type)

These questions are typically asked as MCQs, Assertion-Reason, or one-line answers. They test factual knowledge and basic understanding.

Set A: MCQs and One-Line Answers

Set B: Assertion-Reason Questions

Question 1: Assertion (A): Decomposition of silver chloride into silver and chlorine is a photochemical decomposition reaction. Reason (R): Silver chloride decomposes in the presence of sunlight.
Answer: Both A and R are true and R is the correct explanation of A.

Question 2: Assertion (A): Rusting of iron is a redox reaction. Reason (R): Iron is oxidised and oxygen is reduced in the process.
Answer: Both A and R are true and R is the correct explanation of A.

📖 2 Marks Questions (Short Answer Type I)

These questions require two points or brief explanations and are designed to test conceptual understanding.

Question 1: Why is the amount of gas collected in one test tube double the amount collected in the other during electrolysis of water? Name the gases.

Answer:

• Water (H₂O) contains hydrogen and oxygen in the ratio of 2:1 by volume.

• The gas collected at the cathode is hydrogen (double volume) and at the anode is oxygen (half volume).

Question 2: What is meant by a chemical equation? Why should it be balanced?

Answer:

• A chemical equation is a symbolic representation of a chemical reaction using formulas of reactants and products.

• It should be balanced to satisfy the Law of Conservation of Mass, which states that mass can neither be created nor destroyed.

Question 3: Write the balanced chemical equation for the reaction of iron with steam.

Answer:

• 3Fe + 4H₂O → Fe₃O₄ + 4H₂

• Iron reacts with steam to form iron(II,III) oxide (Fe₃O₄) and hydrogen gas.

Question 4: What is a decomposition reaction? Give one example.

Answer:

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

• Example: CaCO₃ → CaO + CO₂ (on heating).

Question 5: Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

Answer:

• Iron is more reactive than copper, so it displaces copper from copper sulphate solution.

• The blue colour of copper sulphate fades to light green due to the formation of iron sulphate.

Question 6: What is corrosion? Give one example.

Answer:

• Corrosion is the gradual deterioration of a metal due to chemical reactions with the environment.

• Example: Rusting of iron when exposed to moist air.

Question 7: What is rancidity? How can it be prevented?

Answer:

• Rancidity is the oxidation of fats and oils in food, causing unpleasant smell and taste.

• It can be prevented by adding antioxidants, storing food in airtight containers, and refrigeration.

Question 8: Write the chemical equation for the reaction of lead nitrate with potassium iodide.

Answer:

• Pb(NO₃)₂ + 2KI → PbI₂ + 2KNO₃

• A yellow precipitate of lead iodide (PbI₂) is formed.

📖 3 Marks Questions (Short Answer Type II)

These questions require detailed explanations with three distinct points and test analytical understanding.

Question 1: What is a redox reaction? Identify the substance oxidised and reduced in the reaction: MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂.

Answer:

• A redox reaction is a reaction in which oxidation and reduction occur simultaneously.

• HCl is oxidised to Cl₂ (loss of hydrogen), and MnO₂ is reduced to MnCl₂ (gain of hydrogen).

• In terms of electrons, Mn gains electrons (reduced) and Cl loses electrons (oxidised).

Question 2: Explain the process of electrolysis of water with a balanced chemical equation.

Answer:

• Electrolysis of water involves passing electric current through acidified water.

• Water decomposes into hydrogen and oxygen gases: 2H₂O → 2H₂ + O₂.

• Hydrogen collects at the cathode (double volume) and oxygen at the anode (half volume), in a 2:1 ratio.

Question 3: What is meant by a displacement reaction? Explain with an example.

Answer:

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

• Example: Fe + CuSO₄ → FeSO₄ + Cu; iron displaces copper from copper sulphate.

• The blue colour of copper sulphate fades and a brown deposit of copper appears on the iron nail.

Question 4: What is a double displacement reaction? Give an example with a balanced equation.

Answer:

• A double displacement reaction is a reaction in which two compounds exchange ions to form two new compounds.

• Example: AgNO₃ + NaCl → AgCl + NaNO₃; a white precipitate of silver chloride is formed.

• Such reactions often produce a precipitate, making them useful in identifying ions.

Question 5: Explain the terms oxidation and reduction with examples.

Answer:

• Oxidation is the gain of oxygen or loss of hydrogen/electrons; e.g., 2Mg + O₂ → 2MgO.

• Reduction is the loss of oxygen or gain of hydrogen/electrons; e.g., CuO + H₂ → Cu + H₂O.

• Both occur together in a redox reaction, such as the reaction of copper oxide with hydrogen.

Question 6: Why is respiration considered an exothermic reaction? Explain.

Answer:

• Respiration is the breakdown of glucose to release energy in the form of ATP.

• The reaction is C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy.

• Since energy is released during the process, respiration is an exothermic reaction.

Question 7: Explain the process of corrosion of iron and how it can be prevented.

Answer:

• Corrosion of iron, called rusting, occurs when iron reacts with oxygen and moisture to form hydrated iron oxide (Fe₂O₃·xH₂O).

• It can be prevented by painting, oiling, galvanization, and alloying.

• Galvanization involves coating iron with a layer of zinc, which prevents rusting.

Question 8: Explain the process of rancidity and methods to prevent it.

Answer:

• Rancidity is the oxidation of fats and oils in food, causing an unpleasant smell and taste.

• It can be prevented by adding antioxidants like vitamin C and E.

• Storing food in airtight containers, refrigeration, and flushing with nitrogen also prevent rancidity.

Question 9: What is a combination reaction? Give two examples with balanced equations.

Answer:

• A combination reaction is a reaction in which two or more substances combine to form a single product.

• Example 1: CaO + H₂O → Ca(OH)₂ (quicklime + water → slaked lime).

• Example 2: 2Mg + O₂ → 2MgO (magnesium burns in oxygen to form magnesium oxide).

Question 10: Explain the different types of decomposition reactions with examples.

Answer:

• Thermal decomposition: Breaking down by heat, e.g., CaCO₃ → CaO + CO₂.

• Electrolytic decomposition: Breaking down by electricity, e.g., 2H₂O → 2H₂ + O₂.

• Photochemical decomposition: Breaking down by light, e.g., 2AgCl → 2Ag + Cl₂.

Question 11: What happens when dilute hydrochloric acid is added to iron filings? Write the balanced equation.

Answer:

• Hydrogen gas is evolved with a pop sound when a burning splinter is brought near it.

• Iron chloride is formed, and the solution turns light green.

• Balanced equation: Fe + 2HCl → FeCl₂ + H₂.

Question 12: Why do we apply paint on iron articles? Explain.

Answer:

• Paint forms a protective layer on the iron surface, preventing contact with oxygen and moisture.

• This prevents the rusting of iron and increases the life of iron articles.

• It also improves the appearance of the articles.

📖 5 Marks Questions (Long Answer Type)

These questions require comprehensive answers with five distinct points and test in-depth understanding and analytical skills.

Question 1: What is a chemical equation? Explain the steps involved in balancing a chemical equation with an example.

Answer:

• A chemical equation is a symbolic representation of a chemical reaction using formulas of reactants and products.

• It must be balanced to satisfy the Law of Conservation of Mass.

• Steps for balancing: Write the skeletal equation, count atoms of each element, balance one element at a time, and verify the final equation.

• Example: Fe + H₂O → Fe₃O₄ + H₂; balance as 3Fe + 4H₂O → Fe₃O₄ + 4H₂.

• Hit and trial method is commonly used, and fractional coefficients are avoided in the final equation.

Question 2: Explain the different types of chemical reactions with examples.

Answer:

• Combination reaction: Two or more substances combine to form one product, e.g., CaO + H₂O → Ca(OH)₂.

• Decomposition reaction: A single compound breaks into simpler substances, e.g., CaCO₃ → CaO + CO₂.

• Displacement reaction: A more reactive element displaces a less reactive one, e.g., Fe + CuSO₄ → FeSO₄ + Cu.

• Double displacement reaction: Two compounds exchange ions, e.g., AgNO₃ + NaCl → AgCl + NaNO₃.

• Redox reaction: Oxidation and reduction occur together, e.g., CuO + H₂ → Cu + H₂O.

Question 3: Explain oxidation and reduction with examples. What is a redox reaction?

Answer:

• Oxidation is the gain of oxygen or loss of hydrogen/electrons; e.g., 2Mg + O₂ → 2MgO.

• Reduction is the loss of oxygen or gain of hydrogen/electrons; e.g., CuO + H₂ → Cu + H₂O.

• A redox reaction is one in which both oxidation and reduction occur simultaneously.

• Example: ZnO + C → Zn + CO; ZnO is reduced to Zn, and C is oxidised to CO.

• Redox reactions are important in metallurgy, respiration, and corrosion.

Question 4: Explain the process of corrosion and rancidity with examples. How can they be prevented?

Answer:

• Corrosion is the gradual deterioration of metals due to chemical reactions with the environment.

• Example: Rusting of iron forms hydrated iron oxide (Fe₂O₃·xH₂O).

• Prevention: Painting, oiling, galvanization, and alloying.

• Rancidity is the oxidation of fats and oils in food, causing unpleasant smell and taste.

• Prevention: Antioxidants, airtight containers, refrigeration, and nitrogen flushing.

Question 5: Explain the electrolysis of water with a diagram and balanced equation.

Answer:

• Electrolysis of water involves passing electric current through acidified water.

• Water decomposes into hydrogen and oxygen gases: 2H₂O → 2H₂ + O₂.

• Hydrogen collects at the cathode (double volume) and oxygen at the anode (half volume).

• The ratio of hydrogen to oxygen is 2:1 by volume.

• This experiment demonstrates that water is made of hydrogen and oxygen in a fixed ratio.

Question 6: Explain the reaction of metals with acids and write balanced equations.

Answer:

• Metals react with dilute acids to produce hydrogen gas and a salt.

• Example: Zn + 2HCl → ZnCl₂ + H₂; zinc reacts with hydrochloric acid to form zinc chloride and hydrogen.

• Fe + 2HCl → FeCl₂ + H₂; iron reacts with hydrochloric acid to form iron(II) chloride and hydrogen.

• The hydrogen gas evolved burns with a pop sound.

• Copper, silver, and gold do not react with dilute acids as they are less reactive.

Question 7: Explain the process of rusting of iron and the conditions necessary for it.

Answer:

• Rusting is the corrosion of iron in the presence of oxygen and moisture.

• The chemical reaction is: 4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O.

• Conditions necessary: Presence of oxygen, moisture, and an electrolyte (like salt).

• Rusting is faster in coastal areas due to high humidity and salt content.

• Prevention: Painting, oiling, galvanization, and alloying.

Question 8: What are the different types of decomposition reactions? Explain with examples.

Answer:

• Thermal decomposition: Breaking down by heat, e.g., CaCO₃ → CaO + CO₂.

• Electrolytic decomposition: Breaking down by electricity, e.g., 2H₂O → 2H₂ + O₂.

• Photochemical decomposition: Breaking down by light, e.g., 2AgCl → 2Ag + Cl₂.

• These reactions are endothermic as they require energy.

• They are used in industry and daily life, such as in the production of quicklime.

Question 9: Explain the process of displacement and double displacement reactions with examples.

Answer:

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

• Example: Fe + CuSO₄ → FeSO₄ + Cu; iron displaces copper from copper sulphate.

• Double displacement reaction: Two compounds exchange ions to form two new compounds.

• Example: AgNO₃ + NaCl → AgCl + NaNO₃; a white precipitate of silver chloride is formed.

• These reactions are important in industry and laboratory analysis.

Question 10: Explain the importance of chemical equations in chemistry.

Answer:

• Chemical equations represent chemical reactions using formulas of reactants and products.

• They help in understanding the stoichiometry of reactions.

• They are used to calculate the amounts of reactants and products.

• They help in predicting the products of a reaction.

• They are essential in industry, research, and daily life.

Question 11: Explain the reaction of non-metals with oxygen and write balanced equations.

Answer:

• Non-metals react with oxygen to form acidic oxides.

• Example: C + O₂ → CO₂; carbon burns in oxygen to form carbon dioxide.

• S + O₂ → SO₂; sulphur burns in oxygen to form sulphur dioxide.

• These oxides dissolve in water to form acids, e.g., CO₂ forms carbonic acid.

• This is why non-metal oxides are called acidic oxides.

Question 12: Explain the process of oxidation and reduction in terms of electrons.

Answer:

• Oxidation is the loss of electrons, e.g., Zn → Zn²⁺ + 2e⁻.

• Reduction is the gain of electrons, e.g., Cu²⁺ + 2e⁻ → Cu.

• A redox reaction involves both oxidation and reduction.

• Example: Zn + CuSO₄ → ZnSO₄ + Cu; Zn is oxidised and Cu²⁺ is reduced.

• Redox reactions are important in electrochemistry, metallurgy, and biology.

📝 How to Use These PYQs for CBSE Exam Preparation

At Dhingra Classes Nashik, we recommend the following strategies to maximize your score using these PYQs.

🎯 Study Tips

1. 📖 Read each question and try to answer before looking at the solution

2. ✏️ Practice writing answers within time limits (1 mark = 1 min, 3 marks = 5 min, 5 marks = 10 min)

3. 🗣️ Focus on repeated themes like types of reactions, redox reactions, and corrosion

4. 📝 Create flashcards for 1-mark questions

5. ⚗️ Practice balancing equations as many questions require them

6. 🔄 Revise weekly to ensure long-term retention

7. 📋 Practice Assertion-Reason questions as they are frequently asked

8. ✅ Take mock tests using these PYQs

🏫 How Dhingra Classes Nashik Helps Class 10 CBSE Students Master Science

At Dhingra Classes Nashik, we provide comprehensive coaching for Science and all other subjects for Class 10 CBSE students. Our approach includes:

• 📚 Structured Lessons: Teaching concepts with clear explanations

• ⚗️ Equation Practice: Regular practice with balancing equations

• 📝 PYQ Analysis: Regular practice with previous year questions

• ✏️ Regular Tests: Weekly tests to ensure continuous revision

• 🎯 Doubt Clearing Sessions: Personalized attention to every student

• 📊 Progress Tracking: Regular updates to parents about student progress

• 🏆 Answer Writing Practice: Teaching how to structure answers for maximum marks

📞 Contact Dhingra Classes Nashik

• 📱 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 Chemical Reactions and Equations PYQs is essential for Class 10 CBSE students to score high marks in Science board examinations. This comprehensive collection of 1-mark, 2-mark, 3-mark, and 5-mark questions covers all major themes including Chemical Equations, Balancing Equations, Types of Chemical Reactions, Combination Reactions, Decomposition Reactions, Displacement Reactions, Double Displacement Reactions, Redox Reactions, Oxidation, Reduction, Corrosion, and Rancidity.

By regularly practicing these Previous Year Questions and using them in your board exam preparation, you can improve your understanding and score better. At Dhingra Classes Nashik, we are committed to helping Class 10 CBSE students excel in Science and achieve academic success. Remember, Chemical Reactions and Equations is not just about memorizing equations—it is about understanding how substances change and interact in the world around us.