Match the statements in column A with those in column B Column A Column B 1. Coating iron sheets with zinc to prevent rusting (a) Chemical changes 2. A material obtained on melting iron with nickel and chromium (b) Galvanisation 3. A change in which new substances are formed (c) Rust 4. A flaky brown material formed on the surface of iron (d) Crystallisation 5. A process of obtaining pure crystals from impure crystals (e) Stainless steel

1. Galvanisation is the process of applying a protective zinc coating on the surface of steel or iron material to prevent the oxidation of metal surface and from rusting. 2. Stainless steel is an alloy made up of mixtures of elements such as chromium, nickel molybdenum, etc. to prevent it from corrode or rust as occur in case of ordinary steel. 3. Chemical changes are the type of changes where a substance combines with another to form a new substance. This result in change of state as well as chemical composition of new substance. It is irreversible in nature. 4. Rust is an iron oxide, a reddish-brown oxide formed by the oxidation reaction in the presence of water and moist air. 5. Crystallisation is the process by which a solid forms, where the atoms or molecules are highly organised to form a structure known as a crystal. It helps in getting pure form of substance. Column A Column B 1. Coating iron sheets with zinc to prevent rusting (b) Galvanisation 2. A material obtained on melting iron with nickel and chromium (e) Stainless steel 3. A change in which new substances are formed (a) Chemical changes 4. A flaky brown material formed on the surface of the iron (c) Rust 5. A process of obtaining pure crystals from impure crystals (d) Crystallisation

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Learning Elementary Science for Class 7>Chapter 6 - Physical and Chemical Changes>EXERCISES>Q IV

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Rusting of iron takes place in the presence of moist air.

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Important Questions on Physical and Chemical Changes

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Learning Elementary Science for Class 7>Chapter 6 - Physical and Chemical Changes>EXERCISES>Q IV

Magnesium oxide reacts with water to form magnesium hydroxide which is acidic in character.

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When bread goes stale, a physical change takes place.

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Learning Elementary Science for Class 7>Chapter 6 - Physical and Chemical Changes>EXERCISES>Q IV

A reddish deposit formed on an iron nail, when placed in a copper sulphate solution is of iron metal.

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Learning Elementary Science for Class 7>Chapter 6 - Physical and Chemical Changes>EXERCISES>Q IV

The gas produced when washing soda reacts with dilute sulphuric acid is carbon monoxide.

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Learning Elementary Science for Class 7>Chapter 6 - Physical and Chemical Changes>EXERCISES>Q IV

Limewater is a solution of calcium carbonate in water.

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Learning Elementary Science for Class 7>Chapter 6 - Physical and Chemical Changes>EXERCISES>Q IV

Crystallisation is used to obtain pure crystals from impure crystals.

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Learning Elementary Science for Class 7>Chapter 6 - Physical and Chemical Changes>EXERCISES>Q V

Match the statements in column A with those in column B

Column A	Column B
1. Coating iron sheets with zinc to prevent rusting	(a) Chemical changes
2. A material obtained on melting iron with nickel and chromium	(b) Galvanisation
3. A change in which new substances are formed	(c) Rust
4. A flaky brown material formed on the surface of iron	(d) Crystallisation
5. A process of obtaining pure crystals from impure crystals	(e) Stainless steel