Question

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Answer 1

Answer ::

Choose the most appropriate answer.

1. Which of these is a chemical change?

• A substance with different chemical properties is formed ✓
• A substance in a different state but similar chemical properties is formed.
• The molecules of the substance do not undergo any change.
• A substance with a different shape and size but similar chemical properties is formed.

Explanation :-

➳ The properties associated with chemical change which can be determined by chemical reactions are known as chemical properties.

2. Which of these is an irreversible physical change?

• Rusting of iron
• Freezing of water
• A double decomposition reaction
• Breaking of a glass tumbler. ✓

Explanation :-

➳ Breaking of a glass tumbler is a physical change. But when the glass is broken it cannot be reversed to its original form so breaking of a glass tumbler is irreversible change.

3. A arrow pointing downwards in a chemical change shows?

• Evolution of gas
• Forming of precipitate ✓
• Oxidation
• Displacement

Explanation :-

➳ Some chemical reactions are characterized by the formation of an insoluble solid which is known as precipitate.

For example ::

If solution of silver nitrate is added to a solution of sodium chloride, a white precipitate of silver chloride is produced.

• Silver nitrate + Sodium chloride → Silver chloride↓ + Sodium nitrate

4. A chemical reaction in which heat is given out is called

• Exothermic reaction ✓
• Endothermic reaction
• Decomposition reaction
• Neutralization reaction

Explanation :-

➳ A chemical reaction in which heat energy is evolved is called an exothermic reaction.

For example ::

If water is added to quick lime, a large of heat energy is produced along with calcium hydroxide.

[ Quick lime = calcium oxide ]

• Calcium oxide + Water → Calcium hydroxide + heat