Question 2 - Case Based Questions (MCQ) - 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.  

(a) The three constituents of plaque are  

(i) Acid 

(ii) Saliva  

(iii) Bacteria 

(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) 

(b) The pH which leads to tooth decay?  

(i) above 7

(ii) at 7  

(iii) below 5.5 

(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) 

(c) State the time during the day when condition is most favourable for the process of tooth decay.  

(i) 1.0 

(ii) 2.0  

(iii) 3.0 

(iv) 4.0  

Ans.  

According to Table

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

This acid leads to the degradation of teeth.

So, the correct answer is (IV) 

(d) The nature of toothpastes commonly used to  protect tooth decay is:  

(i) acidic 

(ii) basic  

(iii) neutral 

(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)