NCERT Class VII Science Solutions: Chapter 6-Physical and Chemical Changes Part 4

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Question 9:

Explain how painting of an iron gate prevents it from rusting.

Answer:

For rusting, the presence of both oxygen and water (or water vapour) is required. The coat of the paint prevents direct contact of iron with air and oxygen and thus prevents it from rusting.

As showing in images is a painting of an iron gate prevents …

Painting of an Iron Gate Prevents It from Rusting

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Question 10:

Explain why rusting of iron objects is faster in coastal areas than in deserts.

Answer:

For rusting, the presence of both oxygen and moisture (water vapour) is required. In coastal areas the quantity of moisture content in air is high (highly humid) as compared to desert regions (low humid), so the rusting becomes faster in coastal areas.

Question 11:

The gas we use in the kitchen is called liquefied petroleum gas (LPG). In the cylinder it exist as a liquid. When it comes out from the cylinder it becomes a gas (Change – A) then it burns (Change – B). The following statements pertain to these changes. Choose the correct one.

  1. Process – A is a chemical change.

  2. Process – B is a chemical change.

  3. Both processes A and B are chemical changes.

  4. None of these processes is a chemical change.

Answer:

B. Process – B is a chemical change.

As showing in images is a result for lpg

Result for Lpg

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Question 12:

Anaerobic bacteria digest animal waste and produce biogas (Change – A). The biogas is then burnt as fuel (Change – B). The following statements pertain to these changes. Choose the correct one.

  1. Process – A is a chemical change.

  2. Process – B is a chemical change.

  3. Both processes A and B are chemical changes.

  4. None of these processes is a chemical change.

Answer:

C. Both processes A and B are chemical changes.

As showing in images is a result for biogas

Result for Biogas

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