Q. Why is it dangerous to have a charcoal fire burning in a badly ventilated room?
A. The burning charcoal produces carbon monoxide which is a poisonous gas. If there is no escape for the gas, it will fill up the room and suffocate us.
Q. How does a refrigerator keep food fresh?
A. Food remains fresh till the chemical decomposition is caused by the presence of micro-organisms. The function of refrigeration is to maintain low temperatures. The activity of micro-organisms is considerably reduced at lower temperatures and, therefore, food can remain fresh for a considerable length of time.
Q. Why is sea water saline?
A. The rivers have been carrying soluble minerals from the mountains and other areas into the sea throughout the ages. Evaporation does not remove these minerals brought down by rivers. Hence, the sea water is saline, i.e., it contains salts.