1. Candle blows off when covered because it does not get oxygen which helps in burning.
2. When sugar is heated above 200°C it decomposes into carbon and water and therefore sugar gets charred.
3. The mass of an iron rod increases on rusting because rust is hydrated ferric oxide (Fe2O3. 3H2O) which adds to its mass.
4. Salt is mixed with ice while making ice cream because salt causes reduction of temperature and helps to freeze the cream and freezing temperature is lowered from 0°C to 5°C
5. Lactose content of milk undergoes fermentation and changes into lactic acid which on reacting with lactose forms curd.
6. Milk turns sour because the microbes react with milk and grow. They turn lactose into lactic acid which is sour in taste.
7. Sea water boils at a higher temperature than fresh water because Sea water contains impurities which raise the boiling point of water.
8. To sleep under trees at night is dangerous because plants respire at night and give out carbon dioxide which reduces the oxygen content of air required for breathing.
9. Both steam and boiling water have the same temperature i.e. 100oC. But heat content of steam is greater than the boiling water because latent heat of steam is 2.26 x 105 J/kg .That’s why steam produces severe burn as compared to boiling water although both have same temperature.