Tooth enamel is the hardest substance in our body. Name the compound of which it is made up. At what $pH$ of the mouth does it get corroded? State the role of bacteria present in the mouth. Suggest a method to prevent tooth decay.

(N/A) Tooth enamel is made up of $Calcium \text{ } phosphate$ (specifically, $Hydroxyapatite$, a crystalline form of $Calcium \text{ } phosphate$).
It gets corroded when the $pH$ of the mouth falls below $5.5$.
Bacteria present in the mouth produce acids by the degradation of sugar and food particles remaining in the mouth after eating.
To prevent tooth decay, one should use toothpaste, which is generally basic, to neutralize the excess acid produced in the mouth.