NCERT Class VII Science Solutions: Chapter 6-Physical and Chemical Changes Part 2

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Question 7:

Galvanisation is a process used to prevent the rusting of which of the following?

  1. Iron

  2. Zinc

  3. Aluminium

  4. Copper

Answer: A

Image of galvanising process

Image of Galvanising Process

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Question 8:

Paheli s mother made a concentrated sugar syrup by dissolving sugar in hot water. On cooling, crystals of sugar got separated. This Indicates a -

  1. Physical change that can be reversed.

  2. Chemical change that can be reversed.

  3. Physical change that cannot be reversed.

  4. Chemical change that cannot be reversed.

Answer: A

Question 9:

Which of the following statement is incorrect for a chemical reaction?

  1. Heat may be given out but never absorbed.

  2. Sound may be produced.

  3. A colour change may take place.

  4. A gas may be evolved.

Answer: A

Question 10:

Two drops of dilute sulphuric acid were added to 1 g of copper sulphate powder and then small amount of hot water was added to dissolve it (step I). On cooling, beautiful blue coloured crystals got separated (step II). Step I and step II are:

  1. Physical and chemical changes respectively.

  2. Chemical and physical changes respectively.

  3. Both physical change.

  4. Both chemical change.

Answer: C

VERY SHORT ANSWER QUESTIONS

Question 11:

State whether the following statements are True or False:

  1. When a candle burns, both physical and chemical changes take place.

  2. Anaerobic bacteria digest animal waste and produce biogas.

  3. Ships suffer a lot of damage though they are painted.

  4. Stretching of rubber band is not a physical change.

Answer:

  1. When a candle burns, both physical and chemical changes take place. (True)

  2. Anaerobic bacteria digest animal waste and produce biogas. (True)

  3. Ships suffer a lot of damage though they are painted. (True)

  4. Stretching of rubber band is not a physical change. (False)

Question 12:

Melting of wax is a change where a solid changes to liquid state. Give one more such change which you observe in your surroundings.

Answer:

Melting of ice is also a change where solid changes into liquid state.

Question 13:

What kind of change is shown by tearing of paper?

Answer:

Tearing of paper is a physical change although, it cannot be reversed.