Preparing for exams from the beginning of the session is not what students really do and they only study when the tensions of board exams hit them. Then you all know, instead of studying the chapters thoroughly, students look for important questions and answers so that they can prepare themselves with the best.

Not to worry, we are your saviours for tomorrow’s exam. As you all know CBSE is conducting class 10th board exams term 1. The board examination conducted the first exam for class 10th i.e. Social Science yesterday.

Tomorrow is the Science exam and to make it easier for you all who studies at the last moment, we’ve compiled 20 important assertion reason based questions from chapter 1 that can help you top your exam.

Chapter 1 – Chemical Reactions And Equations

In the following questions, a statement of assertion (A) is followed by a statement of the reason (R). Mark the correct choice as:

a) Both A and R are true and R is the correct explanation of A.

(b) Both A and R are true but R is not the correct explanation of A.

(c) A is true but R is false.

(d) A is false but R is true.

1. Assertion (A): Decomposition of vegetable matter into compost is an example of exothermic reactions.

Reason (R): Exothermic reactions are those reactions in which heat is evolved.

2. Assertion (A): When HCl is added to zinc granules, a chemical reaction occurs.

Reason (R): The evolution of a gas and change in colour indicate that the chemical reaction is taking place.

3. Assertion (A): Calcium carbonate when heated gives calcium oxide and water.

Reason (R): On heating calcium carbonate, a decomposition reaction takes place.

4. Assertion (A): Brown fumes are produced when lead nitrate is heated.

Reason (R): Nitrogen dioxide gas is produced as a by-product due to the decomposition of lead nitrate.

5. Assertion (A): White silver chloride turns grey in sunlight.

Reason (R): Decomposition of silver chloride in presence of sunlight takes place to form silver metal and chlorine gas.

6. Assertion (A): Pungent smelling gas is produced when sulphur burns in the air.

Reason (R): Sulphur trioxide is formed on reaction of sulphur with oxygen.

7. Assertion (A): In a reaction of copper with oxygen, copper serves as a reducing agent.

Reason (R): The substance which gains oxygen in a chemical reaction acts as a reducing agent.

8. Assertion (A): In the electrolysis of water, the volume of hydrogen liberated is twice the volume of oxygen ……formed.

Reason (R): Water (H,0) has hydrogen and oxygen in the ratio of 1:2 by volume.

9. Assertion (A): Corrosion of iron is commonly known as rusting.

Reason (R): Corrosion of iron occurs in presence of water and air.

10. Assertion (A): The balancing of chemical equations is based on the law of conservation of mass.

Reason (R): Total mass of reactants is equal to the total mass of products.

11. Assertion (A): In a balanced chemical equation, the total mass of the reactants is equal to the total mass of the products.

Reason (R): Mass can neither be created nor destroyed during a chemical change.

12. Assertion (A): Iron articles are painted so as to prevent them from rusting.

Reason (R): When the surface of iron is coated with paint, its surface does not come in contact with oxygen and moisture therefore rusting does not take place.

13. Assertion (A): Chemical reaction changes the physical and chemical state of a substance.

Reason (R): When an electric current is passed through water (liquid), it decomposes to produce hydrogen and

oxygen gases.

14. Assertion (A): When calcium carbonate is heated, it decomposes to give calcium oxide and carbon dioxide.

Reason (R): The decomposition reaction takes place on the application of heat, therefore, it is an endothermic reaction.

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15. Assertion (A): Zinc reacts with sulphuric acid to form zinc sulphate and hydrogen gas and it is a displacement reaction.

Reason (R): Zinc reacts with oxygen to form zinc oxide.

16. Assertion (A): Chips manufacturers usually Ilush bags of chips with a gas such as nitrogen to prevent the chips from getting oxidised.

Reason (R): This increases the taste of the chips and helps in their digestion.

17. Assertion (A): Exposure of silver chloride to sunlight for a long duration turns grey due to the formation of silver by decomposition of silver chloride.

Reason (R): In this process, sublimation of silver chloride takes place.

18. Assertion (A): Rusting of iron metal is the most common form of corrosion.

Reason (R): The effect of rusting of iron can be reversed if they are left open in sunlight.

19. Assertion (A): AgBr is used on photographic and X-ray film.

Reason (R): AgBr is photosensitive and changes to Ag and bromine in presence of sunlight and undergoes decomposition reaction.

20. Assertion (A): Magnesium ribbon keeps on burning in an atmosphere of nitrogen.

Reason (R): Magnesium reacts with nitrogen to form magnesium nitride and this reaction is a combination reaction.

Answers

1. a
2. b
3. d
4. a
5. a
6. c
7. a
8. c
9. b
10. a
11. a
12. a
13. b
14. b
15. b
16. c
17. c
18. c
19. a
20. a