Q. Why is fire extinguished by sodium bicarbonate?

A. Sodium bicarbonate decomposes on heating to produce carbon dioxide gas. The gas is neither combustible nor a supporter of combustion, so it extinguishes the fire quickly.

Q. What are Gamma Rays?

A. These are short-wave electro-magnetic radiations similar to light and X- rays. The penetrating power of these rays is extremely high, even greater than X- rays. They can penetrate through 6 inches of steel. Gamma rays are not deflected by strong electric or magnetic fields. However, these are harmful to living tissues.

Q. What is a liquid?

A. It is a state of matter intermediate between a gas and a solid. A liquid may be considered as a condensed gas or a molten solid. The molecules are rigidly fixed in a solid and, therefore, it has a definite shape as well as volume. The molecules are free to move in a gas and, therefore, it has neither a definite volume nor a definite shape. The molecules are relatively free to move in a liquid, but this freedom is much more restricted on account of cohesive forces. A liquid, therefore, has a definite volume, but no definite shape. A liquid takes the shape of the vessel in which it is poured. It is only slightly compressible.

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