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Practice Class 10 Science Chapter 1 Chemical Reactions and Equations MCQ Questions with Answers based on the latest NCERT syllabus. Solve advanced MCQs on reaction observations, decomposition reactions, oxidation in daily life, corrosion, and balancing equations with detailed solutions for CBSE, State Board, Olympiad, and scholarship exam preparation.
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Chapter Information
Subject: Science
Class: 10
Chapter: Chemical Reactions and Equations
Question Type: Multiple Choice Questions (MCQs)
Difficulty Level: Moderate to Difficult
Based On: NCERT Latest Syllabus (2026)
Introduction
Chemical reactions are responsible for many changes observed in nature and daily life. From rusting of iron to the digestion of food, these reactions involve the transformation of substances into new products. Understanding reaction observations and chemical equations is essential for mastering chemistry.
What You Will Learn
✔ Observation-based chemistry
✔ Thermal decomposition reactions
✔ Oxidation in daily life
✔ Corrosion and prevention
✔ Balanced chemical equations
✔ Practical chemistry applications
✔ Analytical reasoning skills
Why This Topic Is Important?
Questions related to reaction observations, oxidation, corrosion, and balancing equations are frequently asked in CBSE and State Board examinations. Understanding these concepts helps students solve both theoretical and application-based questions effectively.
1. MCQ Questions with Detailed Solutions
Q1. Which observation is most likely to indicate a chemical reaction?
A) Breaking a wooden stick
B) Formation of a white precipitate
C) Cutting a piece of paper
D) Crushing sugar crystals
Answer
B) Formation of a white precipitate
Concept Behind This Question
Formation of a precipitate indicates the formation of a new substance.
Step-by-Step Solution
A precipitate is an insoluble solid produced during a chemical reaction.
Its formation confirms that a new substance has been formed.
Therefore, the correct answer is:
Formation of a white precipitate
Exam Tip
Precipitate formation is one of the strongest indicators of a chemical reaction.
Q2. Which of the following reactions represents thermal decomposition?
A) $$2AgCl \rightarrow 2Ag + Cl_2$$
B) $$2H_2O \rightarrow 2H_2 + O_2$$
C) $$2Pb(NO_3)_2 \rightarrow 2PbO + 4NO_2 + O_2$$
D) $$Zn + CuSO_4 \rightarrow ZnSO_4 + Cu$$
Answer
C) $$2Pb(NO_3)_2 \rightarrow 2PbO + 4NO_2 + O_2$$
Concept Behind This Question
Thermal decomposition occurs when heat causes a compound to break down.
Step-by-Step Solution
Lead nitrate decomposes on heating:
$$2Pb(NO_3)_2 \rightarrow 2PbO + 4NO_2 + O_2$$
Heat is required for this reaction.
Therefore, it is a thermal decomposition reaction.
Exam Tip
Lead nitrate decomposition is an important NCERT example.
Q3. Which of the following is an example of oxidation in everyday life?
A) Freezing of milk
B) Rusting of iron
C) Breaking of glass
D) Evaporation of water
Answer
B) Rusting of iron
Concept Behind This Question
Oxidation involves the addition of oxygen.
Step-by-Step Solution
Iron reacts with oxygen and moisture to form rust.
This process involves oxidation.
Therefore, rusting is an example of oxidation.
Exam Tip
Rusting is one of the most frequently asked examples of oxidation.
Q4. Which gas is released during the thermal decomposition of lead nitrate?
A) Hydrogen
B) Nitrogen
C) Nitrogen Dioxide
D) Helium
Answer
C) Nitrogen Dioxide
Useful Concept for this Question
Lead nitrate decomposition produces brown fumes of nitrogen dioxide.
Step-by-Step Solution
Reaction:
$$2Pb(NO_3)_2 \rightarrow 2PbO + 4NO_2 + O_2$$
The gas $$NO_2$$ is nitrogen dioxide.
It appears as brown fumes.
Therefore, the correct answer is nitrogen dioxide.
Exam Tip
Brown fumes in laboratory reactions often indicate nitrogen dioxide gas.
Q5. Which method protects iron by coating it with zinc?
A) Painting
B) Alloying
C) Galvanization
D) Greasing
Answer
C) Galvanization
Concept Behind This Question
Galvanization prevents rusting by applying a zinc layer.
Step-by-Step Solution
A protective zinc coating prevents oxygen and moisture from reaching iron.
Thus, rust formation is reduced.
Therefore, the correct answer is galvanization.
Exam Tip
Galvanization is one of the most important corrosion-prevention methods.
Important Formulas & Concepts
1. Thermal Decomposition
A compound breaks down when heated.
Example:
$$2Pb(NO_3)_2 \rightarrow 2PbO + 4NO_2 + O_2$$
2. Oxidation
Addition of oxygen or removal of hydrogen.
3. Precipitate
An insoluble solid formed during a reaction.
4. Corrosion
Gradual destruction of metals due to environmental reactions.
5. Galvanization
Protection of iron by coating it with zinc.
Related Practice Questions
- What is thermal decomposition?
- Why is rusting considered oxidation?
- What is a precipitate?
- Which gases are produced when lead nitrate decomposes?
- How does galvanization prevent rusting?
Mini Quiz Challenge
Fill in the blanks
- Lead nitrate decomposes when __________ is supplied.
- Rusting is an example of __________.
- Iron is protected from rusting by __________.
Answers
- Heat
- Oxidation
- Galvanization
Exam Tips
✔ Learn important decomposition reactions from NCERT.
✔ Revise common examples of oxidation.
✔ Remember laboratory observations such as brown fumes.
✔ Practice identifying reaction indicators.
✔ Understand corrosion-prevention methods.
Quick Revision Notes
✔ Precipitate formation indicates a chemical reaction.
✔ Lead nitrate undergoes thermal decomposition.
✔ Nitrogen dioxide appears as brown fumes.
✔ Rusting is an oxidation process.
✔ Galvanization protects iron from corrosion.
✔ Heat can cause decomposition reactions.
✔ New substances are formed during chemical reactions.
Common Mistakes Students Make
❌ Confusing thermal decomposition with photochemical decomposition.
❌ Forgetting the products of lead nitrate decomposition.
❌ Mixing oxidation with corrosion.
❌ Ignoring reaction observations.
❌ Memorizing equations without understanding concepts.
Key Takeaways
✔ Formation of a precipitate indicates a chemical reaction.
✔ Lead nitrate decomposes when heated.
✔ Nitrogen dioxide gas appears as brown fumes.
✔ Rusting is a common oxidation reaction.
✔ Galvanization prevents corrosion.
✔ Understanding observations improves chemistry problem-solving.
FAQs
1. What is thermal decomposition?
The breakdown of a compound by heating.
2. What is a precipitate?
An insoluble solid formed during a chemical reaction.
3. Why does lead nitrate produce brown fumes?
Because nitrogen dioxide gas is released.
4. What is galvanization?
Coating iron with zinc to prevent rusting.
5. Why is rusting an oxidation reaction?
Because iron combines with oxygen during rust formation.
Conclusion
Chemical reactions can be identified through observations such as precipitate formation, gas evolution, and colour changes. Understanding thermal decomposition, oxidation, corrosion, and galvanization helps students strengthen their chemistry concepts and perform better in examinations.
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