Tooth decay starts when the p4 of the mouth is lower than 5.5. Tooth enamel, made up of calcium hydroxyapatite (a crystalline form of calcium phosphate) is the hardest substance in the body. It does not dissolve in water, but is corroded when the pH in the mouth is below 5.5. Bacteria present in the mouth produce acids by degradation of sugar and food particles remaining in the mouth after eating. The best way to prevent this is to clean the mouth after eating food. Using toothpastes, which are generally basic, for cleaning the teeth can neutralise the excess acid and prevent tooth decay.1. pH of the mouth should be within(i) 7.6 - 8.2(ii) 6.2 - 7.6(iii) 5.6 - 6.2(iv) 5.52. True or false. During tooth decay, basic substances are used to increase the pH of the mouth.(i) TRUE(ii) FALSE3. Bacteria present in the mouth produce _____ by degradation of sugar and food particles remaining in the mouth after eating.(i) Acids(ii) Base(iii) Salts(iv) None of theseQ 4. Prevention of tooth decay can be done by-(i) Clean the mouth before eating(ii) Clean the mouth after eating(iii) Drink water to remove germs(iv) Gargle mouth with HCl5. True or false. Tooth decay starts when the pH of the mouth is higher than 5.5.(i) TRUE(ii) FALSE