Following questions consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate option given below:
(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.
Q.1. Assertion (A) : Decomposition of vegetable matter into compost is an example of exothermic reactions.
Reason (R) : Exothermic reaction are those reactions in which heat is evolved.
Q.2. Assertion (A) : When HCl is added to zinc granules, a chemical reaction occurs.
Reason (R) : Evolution of a gas and change in colour indicate that the chemical reaction is taking place.
Q.3. Assertion (A) : Calcium carbonate when heated gives calcium oxide and water.
Reason (R) : On heating calcium carbonate, decomposition reaction takes place.
Q.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.
Q.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.
Q.6. Assertion (A): Pungent smelling gas is produced when sulphur burns in air.
Reason (R) : Sulphur trioxide is formed on reaction of sulphur with oxygen.
Q.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.
Q.8. Assertion (A) : In 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.
Q.9. Assertion (A): Corrosion of iron is commonly known as rusting.
Reason (R) : Corrosion of iron occurs in presence of water and air.
Q.10. Assertion (A) : The balancing of chemical equations is based on law of conservation of mass.
Reason (R) : Total mass of reactants is equal to total mass of products.
Q.11. Assertion (A): In a balanced chemical equation, 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.
Answer(a) This is due to the conservation of mass.
Q.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.
Q.13. Assertion (A) : Chemical reaction changes the physical and chemical state of a substance.
Reason (R) : When electric current is passed through water (liquid), it decomposes to produce hydrogen and
Q.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 application of heat, therefore, it is an endothermic reaction.
Answer(b) CaCO3 on heating gives CO2 and CaO.
Q.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
Answer(b) Decomposition reaction is a reaction in which a compound breaks down into two or more simpler substances.
Q.16. Assertion (A): Chips manufacturers usually Ilush bags of chips with gas such as nitrogen to prevent the chips from getting oxidised.
Reason (R): This increase the taste ot the chips and helps in their digestion.
Answer(c) Nitrogen being antioxidant prevents the chips from being oxidised.
Q.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.
Q.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.
Q.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
Answer(a) AgBr is a chemical compound. It is widely used in photography as photographic emulsions.
Q.20. Assertion (A): Magnesium ribbon keeps on burning in atmosphere of nitrogen.
Reason (R) : Magnesium reacts with nitrogen to form magnesium nitride and this reaction is combination reaction.
Q.21. Assertion (A): A lead nitrate on thermal decomposition gives lead oxide, brown coloured nitrogen dioxide and oxygen gas.
Reason (R): Lead nitrate reacts with potassium iodide to form yellow ppt. of lead iodide and the reaction is double displacement as well as precipitation reaction.