Explain the pH change as the cause of tooth decay. How can tooth decay caused by pH change be prevented? (b) Explain how pH change in the lake water can endanger the lives of aquatic animals (like fish). What can be done to lessen the danger to the lives of aquatic animals in the lake?

(a)Tooth is made up of calcium phosphate and enamel is the hardest part in our body it covers the surface of teeth. If the pH in the mouth is below 5.5 it causes acidity and tooth decay starts. Acid have the power of decaying any material if it is hard even. It can be prevented by our self by brushing every two times a day after having food. Before going to bed is necessary because bacterial action can takes place easily while sleeping. Toothpaste containing more basicity can be used for brushing the teeth.

(b) pH of water contains 7. The Rain water is 5.6 because of acid rain, the acidity of river and lake water increases. The animals living in water feels more difficulty in living in water having low pH. In order to prevent the acidity bases like calcium carbonate can be added to the water hence it neutralises the excess acidity caused by the acid rain.