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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 precipitation reactions, thermal decomposition, rancidity, redox reactions, and chemical changes with detailed step-by-step 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 play a vital role in everyday life. Many useful products are formed through chemical reactions, while some reactions can cause damage to materials. Understanding different reaction types helps students identify chemical changes and apply scientific concepts to real-life situations.
What You Will Learn
✔ Precipitation reactions
✔ Thermal decomposition
✔ Redox reactions
✔ Rancidity
✔ Characteristics of chemical reactions
✔ Practical applications of chemistry
✔ Problem-solving using chemical equations
Why This Topic Is Important?
Chemical reactions are used in industries, medicine, agriculture, food preservation, and environmental science. This chapter forms the foundation for higher studies in chemistry and helps students answer application-based questions in examinations.
1. MCQ Questions with Detailed Solutions
Q1. Which of the following reactions produces a precipitate?
A) $$AgNO_3 + NaCl \rightarrow AgCl + NaNO_3$$
B) $$CH_4 + O_2 \rightarrow CO_2 + H_2O$$
C) $$2Mg + O_2 \rightarrow 2MgO$$
D) $$CaCO_3 \rightarrow CaO + CO_2$$
Answer
A) $$AgNO_3 + NaCl \rightarrow AgCl + NaNO_3$$
Concept Behind This Question
A precipitate is an insoluble solid formed during a chemical reaction.
Step-by-Step Solution
When silver nitrate reacts with sodium chloride:
$$AgNO_3 + NaCl \rightarrow AgCl + NaNO_3$$
Silver chloride ($$AgCl$$) appears as a white insoluble solid.
Therefore, this is a precipitation reaction.
Exam Tip
Whenever an insoluble solid forms in a solution, a precipitate reaction has occurred.
Q2. Which gas is produced during the thermal decomposition of calcium carbonate?
$$CaCO_3 \rightarrow CaO + ?$$
A) Oxygen
B) Hydrogen
C) Carbon Dioxide
D) Nitrogen
Answer
C) Carbon Dioxide
Useful Concept for this Question
Thermal decomposition occurs when heat breaks a compound into simpler substances.
Step-by-Step Solution
The decomposition reaction is:
$$CaCO_3 \rightarrow CaO + CO_2$$
The gas released is carbon dioxide.
Therefore, the correct answer is Carbon Dioxide.
Exam Tip
Limestone decomposition is a commonly asked NCERT reaction.
Q3. Which of the following is an example of a redox reaction?
A) $$HCl + NaOH \rightarrow NaCl + H_2O$$
B) $$CuO + H_2 \rightarrow Cu + H_2O$$
C) $$CaO + H_2O \rightarrow Ca(OH)_2$$
D) $$NaCl \rightarrow Na + Cl$$
Answer
B) $$CuO + H_2 \rightarrow Cu + H_2O$$
Concept Behind This Question
A redox reaction involves oxidation and reduction occurring simultaneously.
Step-by-Step Solution
In the reaction:
$$CuO + H_2 \rightarrow Cu + H_2O$$
Hydrogen gains oxygen and gets oxidized.
Copper oxide loses oxygen and gets reduced.
Therefore, it is a redox reaction.
Exam Tip
Remember: Oxidation and reduction always occur together in redox reactions.
Q4. What is rancidity?
A) Formation of salt
B) Spoilage of food due to oxidation
C) Decomposition by heat
D) Formation of precipitate
Answer
B) Spoilage of food due to oxidation
Concept Behind This Question
Fats and oils react with oxygen and develop an unpleasant smell and taste.
Step-by-Step Solution
Rancidity occurs when food containing fats and oils gets oxidized.
This leads to:
• Bad smell
• Unpleasant taste
• Loss of food quality
Therefore, the correct answer is spoilage of food due to oxidation.
Exam Tip
Nitrogen-filled packets are used to prevent rancidity in chips and snacks.
Q5. Which observation confirms that a chemical reaction has taken place?
A) Change in colour
B) Evolution of gas
C) Formation of precipitate
D) All of these
Answer
D) All of these
Useful Concept for this Question
Several indicators help identify a chemical reaction.
Step-by-Step Solution
Common signs of chemical reactions include:
• Colour change
• Gas evolution
• Formation of precipitate
• Temperature change
Since all options indicate a chemical reaction,
the correct answer is:
All of these
Exam Tip
Learn all indicators of chemical reactions for board exams.
Important Formulas & Concepts
1. Precipitation Reaction
Formation of an insoluble solid during a reaction.
2. Thermal Decomposition
A compound breaks down on heating.
Example:
$$CaCO_3 \rightarrow CaO + CO_2$$
3. Redox Reaction
Oxidation and reduction occur simultaneously.
4. Rancidity
Oxidation of fats and oils causing food spoilage.
5. Indicators of Chemical Reactions
• Colour change
• Gas evolution
• Precipitate formation
• Temperature change
Related Practice Questions
- What is a precipitation reaction?
- Define rancidity with one example.
- Why are redox reactions important?
- What products are formed when calcium carbonate is heated?
- Name three indicators of a chemical reaction.
Mini Quiz Challenge
Fill in the blanks
- Silver chloride is a __________ precipitate.
- Rancidity occurs due to __________.
- A reaction involving oxidation and reduction is called a __________ reaction.
Answers
- White
- Oxidation
- Redox
Exam Tips
✔ Learn all NCERT chemical equations.
✔ Understand the meaning of oxidation and reduction.
✔ Revise examples of precipitation reactions.
✔ Remember methods used to prevent rancidity.
✔ Focus on reaction observations and indicators.
Quick Revision Notes
✔ Precipitation reactions form insoluble solids.
✔ Calcium carbonate decomposes into calcium oxide and carbon dioxide.
✔ Redox reactions involve oxidation and reduction together.
✔ Rancidity causes food spoilage.
✔ Colour change often indicates a chemical reaction.
✔ Gas evolution is a common sign of chemical change.
✔ Chemical reactions create new substances.
Common Mistakes Students Make
❌ Confusing precipitation reactions with combination reactions.
❌ Forgetting the products of thermal decomposition.
❌ Mixing oxidation and reduction definitions.
❌ Ignoring practical examples of rancidity.
❌ Memorizing reactions without understanding concepts.
Key Takeaways
✔ Precipitation reactions produce insoluble solids.
✔ Thermal decomposition requires heat energy.
✔ Redox reactions involve simultaneous oxidation and reduction.
✔ Rancidity is caused by oxidation of fats and oils.
✔ Chemical reactions can be identified through observable changes.
✔ Understanding reaction indicators improves conceptual clarity.
FAQs
1. What is a precipitate?
An insoluble solid formed during a chemical reaction.
2. What is thermal decomposition?
Breaking a compound into simpler substances using heat.
3. What is a redox reaction?
A reaction where oxidation and reduction occur together.
4. Why does food become rancid?
Due to oxidation of fats and oils.
5. How can rancidity be prevented?
By storing food in airtight containers and reducing exposure to oxygen.
Conclusion
Chemical Reactions and Equations is an important chapter that explains how substances change during chemical processes. Understanding precipitation reactions, thermal decomposition, redox reactions, and rancidity helps students apply chemistry concepts in real-life situations and perform better in examinations.
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