What is the pH value of the saliva before and after a meal ?

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5, 7.4

7, 10

7.4, 5.8

2, 5

answer is C.

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Detailed Solution

Concept- A healthy mouth has neutral pH. But intake of food causes a decrease in pH.
Our teeth are mainly made up of calcium. At a pH below 5.5, bacterial growth in the mouth increases and the tooth starts decaying.
Now, the pH of saliva is 7.4 at

25^{0} C

, which is alkaline in nature. After a meal, this pH decreases to 5.8. Now,the tooth decay begins when the pH in the mouth is lower than 5.5. As acidic environments corrode tooth enamel and eventually weaken it, thus to prevent the decay of tooth enamel, toothpaste should be basic in nature.
Therefore, toothpaste, which is generally alkaline, can neutralise excess acid and prevent tooth decay.
Hence, the correct option is (3).

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