Case Based Questions (MCQ)

Class 10
Chapter 2 Class 10 - Acids, Bases and Salts

## Study the given table and answer the following  questions. It shows the pH value of the plaque  (which collects around teeth) surrounding the  teeth of a child over 3 hrs.

 Time/h pH 0.00 7.0 1.0 7.0 2.0 7.1 3.0 7.2 4.0 4.1

## (iv) All of these

Ans.

Plaque is a sticky film that coats the teeth.

It contains

• Bacteria
• Acid
• Saliva
• Food

So, the correct answer is (iv)

## (iv) above 5.5

Ans.

The consumption of acidic food and drinks leads to the degradation of teeth leading to plaque formation.

Since acidic foods have pH less than 7.

So, the correct answer is (iii)

## (iv) 4.0

Ans.

According to Table

 Time/h pH 0.00 7.0 1.0 7.0 2.0 7.1 3.0 7.2 4.0 4.1

At Time 4.0, the pH is lowest , which indicates the highest amount of acid produced by the bacteria.

So, the correct answer is (IV)

## (iv) none of the above

Ans.

Since tooth decay is caused due to the acids produced by bacteria, in order to prevent it, we use basic toothpaste.

Since Base neutralises the Acid , toothpastes usually have a mild base as its ingredient.

So, the correct answer is (ii)