Q20 of 38 Page 32

Why is the use of diesel and petrol as fuels in automobiles being replaced by Compressed Natural Gas (CNG) in big cities?

Fuels like petrol and diesel give away a lot of smoke when heated, thus causing pollution. CNG is an environment friendly fuel and does not play a role in the increase of pollution. CNG produces harmful products in a very small quantity.


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18

Two glass jars A and B are filled with carbon dioxide and oxygen gases, respectively. In each jar a lighted candle is placed simultaneously. In which jar will the candle remain lighted for a longer time and why?

 19

Anu wants to boil water quickly in a test tube. On observing the different zones of the flame, she is not able to decide which zone of the flame will be best for boiling water quickly. Help her in this activity.

 21

Boojho wants to separate the following materials as combustible and non-combustible. Can you help him?

Charcoal, chalk, stone, iron rod, copper coin, straw, cardboard, glass, paper, candle, wood.

 22

Indicate whether the following statements are True or False. Also write the false statements in their correct form.

(a) Air is necessary for combustion.


(b) Magnesium is a non-combustible metal.


(c) Carbon dioxide is an excellent fire extinguisher.


(d) Calorific value of wood is higher than that of coal.