Question : Why do we perspire on a hot day?
Answer : When the body temperature rises, the sweat glands are stimulated to secrete perspiration. It is nature’s way to keep the body cool. During the process of evaporation of sweat, body heat is taken away, thus, giving a sense of coolness.

Question : Why does the mass of an iron rod increase on rusting?
Answer : Because rust is hydrated ferric oxide which adds to the mass of the iron rod. The process of rusting involves addition of hydrogen and oxygen elements to iron.

Question : Why does milk curdle?
Answer : Lactose (milk sugar) content of milk undergoes fermentation and changes into lactic acid which on reacting forms curd.

Question : Why does not hard water lather soap profusely?
Answer : Hard water contains sulfates and chlorides of magnesium and calcium which forms an insoluble compound with soap. Therefore, soap does not lather with hard water.

Question : Why is it dangerous to have charcoal fire burning in a closed room?
Answer : When charcoal bums it produces carbon monoxide which is suffocating and can cause death.

Question : Why is it dangerous to sleep under trees at night?
Answer : Plants respire at night and give out carbon dioxide which reduces the oxygen content of air required for breathing.

Question : Why does ENO’s salt effervesce on addition of water?
Answer : It contains tartaric acid and sodium bicarbonate. On adding water, carbon dioxide is produced which when released into water causes effervescence.

Question : Why does milk turn sour?
Answer : The microbes react with milk and grow. They turn lactose into lactic acid which is sour in taste.

Question : Why is a new quilt warmer than an old one?
Answer : In a new quilt the cotton is not compressed and as such it encloses more air which is bad conductor of heat. Therefore, it does not allow heat to pass.

Question : Eskimos live in double-walled ice houses. Why?
Answer : Because the air in between two ice walls does not allow heat to pass.