Assertion and Reason set based on NCERT Class 10 Science Chapter 1: Chemical Reactions and Equations.

Assertion Class 10

Assertion and Reason Type Questions

Each question consists of an Assertion (A) and a Reason (R). Choose the correct option:

• (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
• (B) Both the Assertion and the Reason are correct, but the Reason does not properly explain the Assertion.
• (C) Assertion is true, but Reason is false.
• (D) Assertion is false, but Reason is true.

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Basic Concepts of Chemical Reactions

1. (A): A chemical equation must be balanced.
   (R): A balanced chemical equation follows the law of conservation of mass.
2. (A): A balanced chemical equation represents the actual number of atoms involved in a reaction.
   (R): The mass of reactants and products must be equal in a chemical reaction.
3. (A): A chemical reaction occurs when reactants are converted into products.
   (R): During a reaction, chemical bonds in reactants are broken and new bonds are formed to create products.
4. (A): Magnesium ribbon is cleaned before burning in air.
   (R): Magnesium reacts with atmospheric oxygen and forms a protective oxide layer that must be removed before burning.
5. (A): Chemical reactions always produce a gas.
   (R): All chemical reactions result in a change in physical state.

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Types of Chemical Reactions

6. (A): The reaction of sodium with water is highly exothermic.
   (R): Sodium reacts with water to form sodium hydroxide and hydrogen gas, releasing heat.
7. (A): A decomposition reaction requires an external energy source.
   (R): Decomposition reactions break down a single compound into two or more simpler substances.
8. (A): Combination reactions always release energy.
   (R): In a combination reaction, two or more substances react to form a single product.
9. (A): The rusting of iron is an example of a combination reaction.
   (R): Rust is formed when iron combines with oxygen and water.
10. (A): The reaction between iron and copper sulphate is a displacement reaction.
    (R): A more reactive metal displaces a less reactive metal from its salt solution.
11. (A): All decomposition reactions require heat, light, or electricity.
    (R): Decomposition reactions break down compounds into simpler substances.
12. (A): The reaction between barium chloride and sodium sulphate is a double displacement reaction.
    (R): This reaction produces a precipitate of barium sulphate.
13. (A): In an exothermic reaction, heat is absorbed.
    (R): Energy is required to break chemical bonds in exothermic reactions.
14. (A): In a neutralization reaction, heat is always released.
    (R): Neutralization reactions involve the combination of acids and bases to form salt and water.
15. (A): Respiration is an exothermic reaction.
    (R): During respiration, glucose is broken down in the presence of oxygen to release energy.

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Oxidation and Reduction

16. (A): Rusting of iron is an oxidation reaction.
    (R): Iron reacts with oxygen and water to form hydrated iron oxide.
17. (A): When zinc is added to copper sulphate solution, zinc displaces copper.
    (R): Zinc is more reactive than copper in the reactivity series.
18. (A): A substance that gains oxygen is said to be oxidized.
    (R): Oxidation is the process of losing electrons.
19. (A): Reduction is the gain of hydrogen.
    (R): Reduction involves the loss of electrons.
20. (A): In the reaction , copper is oxidized.
    (R): Hydrogen removes oxygen from copper oxide, forming copper metal.
21. (A): Photosynthesis is an oxidation-reduction reaction.
    (R): Carbon dioxide is reduced to glucose, and water is oxidized to oxygen.
22. (A): The burning of coal is an oxidation reaction.
    (R): Carbon reacts with oxygen to form carbon dioxide, releasing heat.
23. (A): Corrosion is a redox reaction.
    (R): Metals lose electrons when they react with oxygen and water.
24. (A): Silver articles turn black due to oxidation.
    (R): Silver reacts with hydrogen sulphide in the air to form silver sulphide.
25. (A): The reaction of iron with hydrochloric acid is an example of oxidation.
    (R): Iron donates electrons to hydrogen ions, forming iron chloride and hydrogen gas.

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Chemical Changes and Applications

26. (A): Rancidity occurs when fats and oils react with oxygen.
    (R): Flushing food with nitrogen gas prevents rancidity.
27. (A): Corrosion can be prevented by galvanization.
    (R): Galvanization involves coating iron with zinc to prevent rusting.
28. (A): Precipitation reactions are examples of double displacement reactions.
    (R): Precipitation occurs when two aqueous solutions react to form an insoluble solid.
29. (A): All combination reactions are exothermic.
    (R): Some combination reactions, such as the formation of nitric acid, absorb heat.
30. (A): Fermentation is an oxidation reaction.
    (R): Fermentation is a process in which sugars are broken down, resulting in the formation of alcohol and carbon dioxide.

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Advanced Concepts

31. (A): Decomposition of silver bromide is a photochemical reaction.
    (R): Silver bromide breaks down in the presence of sunlight.
32. (A): The electrolysis of water produces hydrogen and oxygen in a 2:1 ratio.
    (R): Water consists of two hydrogen atoms and one oxygen atom.
33. (A): A catalyst speeds up a reaction by increasing activation energy.
    (R): Catalysts provide an alternative pathway with lower activation energy.
34. (A): The reaction between calcium carbonate and hydrochloric acid produces carbon dioxide.
    (R): Acid reacts with carbonate compounds to release CO₂.
35. (A): When a lead-acid battery is discharged, lead sulphate forms.
    (R): Lead sulphate formation is a reversible reaction.
36. (A): Endothermic reactions absorb heat.
    (R): Photosynthesis is an endothermic process.
37. (A): All redox reactions involve oxidation and reduction occurring simultaneously.
    (R): Electrons lost in oxidation are gained in reduction.
38. (A): A precipitation reaction always produces gas.
    (R): Precipitation reactions result in an insoluble solid formation.
39. (A): Anodizing protects aluminum from corrosion.
    (R): Anodizing increases the thickness of the oxide layer on aluminum.
40. (A): Neutralization reactions always involve an acid and a base.
    (R): A neutralization reaction produces salt and water.

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