Question

1. Burning of fuel is a desirable change. 2. Rotation of the Earth is a periodic change. 3. Melting of butter is a physical change. 4. Generally physical changes are easier to reverse while chemical changes are not 5. Boiling of water is a physical change but boiling of egg is a chemical change. ​

Answer 1

Answer:

The burning of fuels like wood, coal or petrol is both desirable and undesirable change. The burning of fuels produce heat which is desirable but the burning also produce smoke. It pollutes the atmosphere and is undesirable.

Answer 2

Answer:

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Explanation:

ANSWER

1.The burning of fuels like wood, coal or petrol is both desirable and undesirable change. The burning of fuels produce heat which is desirable but the burning also produce smoke. It pollutes the atmosphere and is undesirable.

2.The motion of the Earth round the sun is periodic because it always completes one revolution in one year. The motion of the earth rotating on its axis once in 24 hours is a kind of periodic motion because the time duration of 24 hours is fixed.