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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 challenging MCQs on decomposition by heat, reaction energy changes, oxidation, corrosion, and chemical equation concepts with detailed solutions for CBSE, State Board, Olympiad, and scholarship exams.
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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 can occur due to heat, light, electricity, or direct contact between substances. These reactions may release energy, absorb energy, or produce entirely new substances. Understanding their behavior helps students explain many scientific and everyday phenomena.
What You Will Learn
✔ Thermal decomposition reactions
✔ Exothermic and endothermic reactions
✔ Oxidation and reduction concepts
✔ Corrosion-related applications
✔ Chemical equation analysis
✔ Real-life chemistry applications
✔ Higher-order reasoning skills
Why This Topic Is Important?
Chemical reactions are the basis of industrial processes, energy production, food preservation, and environmental changes. A strong understanding of reaction types helps students perform well in school examinations and competitive tests.
1. MCQ Questions with Detailed Solutions
Q1. Which of the following compounds decomposes on heating?
A) $$NaCl$$
B) $$CaCO_3$$
C) $$Cu$$
D) $$Fe$$
Answer
B) $$CaCO_3$$
Concept Behind This Question
Some compounds break into simpler substances when heated.
Step-by-Step Solution
When calcium carbonate is heated:
$$CaCO_3 \rightarrow CaO + CO_2$$
This is a thermal decomposition reaction.
Therefore, the correct answer is:
Calcium Carbonate
Exam Tip
Thermal decomposition reactions require heat energy.
Q2. Which reaction absorbs energy from the surroundings?
A) Exothermic Reaction
B) Combustion Reaction
C) Endothermic Reaction
D) Respiration Reaction
Answer
C) Endothermic Reaction
Concept Behind This Question
Endothermic reactions require energy to proceed.
Step-by-Step Solution
In endothermic reactions:
• Heat is absorbed
• Surroundings become cooler
• Energy enters the system
Therefore, the correct answer is:
Endothermic Reaction
Exam Tip
Remember:
Exothermic → Releases heat
Endothermic → Absorbs heat
Q3. Which substance is oxidized in the reaction?
$$2Mg + O_2 \rightarrow 2MgO$$
A) Oxygen
B) Magnesium
C) Magnesium Oxide
D) None of these
Answer
B) Magnesium
Useful Concept for this Question
Oxidation means addition of oxygen.
Step-by-Step Solution
Magnesium combines with oxygen:
$$Mg + O \rightarrow MgO$$
Since magnesium gains oxygen, it is oxidized.
Therefore, the correct answer is magnesium.
Exam Tip
The substance gaining oxygen is always oxidized.
Q4. Which metal object is most likely to rust quickly?
A) Iron kept in dry air
B) Iron coated with paint
C) Iron kept in moist air
D) Galvanized iron
Answer
C) Iron kept in moist air
Concept Behind This Question
Rusting requires both oxygen and moisture.
Step-by-Step Solution
Moist air provides:
• Oxygen
• Water vapour
Both are necessary for rust formation.
Therefore, iron kept in moist air rusts fastest.
Exam Tip
Without moisture, rusting occurs very slowly.
Q5. Which statement about a balanced chemical equation is correct?
A) Number of compounds must be equal
B) Number of molecules must be equal
C) Number of atoms of each element must be equal
D) Number of products must equal number of reactants
Answer
C) Number of atoms of each element must be equal
Concept Behind This Question
Balanced equations obey the law of conservation of mass.
Step-by-Step Solution
A balanced equation requires:
• Equal atoms of every element
• Equal mass on both sides
The number of compounds does not need to be the same.
Therefore, the correct answer is:
Number of atoms of each element must be equal
Exam Tip
Always count atoms element-wise while balancing equations.
Important Formulas & Concepts
1. Thermal Decomposition
A compound breaks down on heating.
Example:
$$CaCO_3 \rightarrow CaO + CO_2$$
2. Endothermic Reaction
A reaction that absorbs heat energy.
3. Exothermic Reaction
A reaction that releases heat energy.
4. Oxidation
Addition of oxygen or removal of hydrogen.
5. Conditions for Rusting
• Oxygen
• Moisture
Related Practice Questions
- What is thermal decomposition?
- Define endothermic reaction with an example.
- Why is magnesium oxidized when burned?
- What conditions are necessary for rusting?
- Why must chemical equations be balanced?
Mini Quiz Challenge
Fill in the blanks
- Calcium carbonate decomposes on __________.
- Endothermic reactions __________ heat.
- Rusting requires oxygen and __________.
Answers
- Heating
- Absorb
- Moisture
Exam Tips
✔ Learn examples of thermal decomposition reactions.
✔ Revise exothermic and endothermic reactions together.
✔ Understand oxidation using reaction examples.
✔ Remember the conditions required for rusting.
✔ Practice balancing equations regularly.
Quick Revision Notes
✔ Calcium carbonate decomposes on heating.
✔ Endothermic reactions absorb energy.
✔ Magnesium gains oxygen during oxidation.
✔ Moisture accelerates rusting.
✔ Balanced equations have equal atoms on both sides.
✔ Heat can initiate chemical reactions.
✔ Oxidation is a common chemical process.
Common Mistakes Students Make
❌ Confusing endothermic and exothermic reactions.
❌ Forgetting the conditions required for rusting.
❌ Mixing oxidation and reduction concepts.
❌ Ignoring atom counting while balancing equations.
❌ Memorizing equations without understanding reaction types.
Key Takeaways
✔ Heat can cause decomposition reactions.
✔ Endothermic reactions absorb energy.
✔ Oxidation involves gain of oxygen.
✔ Rusting occurs faster in moist conditions.
✔ Balanced equations follow conservation of mass.
✔ Understanding reaction energy helps identify reaction types.
FAQs
1. What is thermal decomposition?
The breakdown of a compound due to heating.
2. What is an endothermic reaction?
A reaction that absorbs heat from the surroundings.
3. Why is magnesium oxidized when burned?
Because it combines with oxygen.
4. What conditions are necessary for rusting?
Presence of oxygen and moisture.
5. Why are balanced equations important?
They ensure the law of conservation of mass is satisfied.
Conclusion
Chemical reactions can release or absorb energy and may occur due to heat, light, or electricity. Understanding thermal decomposition, oxidation, rusting, and balanced equations helps students develop strong chemistry concepts and perform confidently in examinations.
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