Question

A solution has turned the colour of the red litmus paper to blue. The pH of the solution is approximately :

• A. 2
• B. 5
• C. 7
• D. 10

Answer 1

The correct option is D

10

Litmus paper

1. Litmus paper is an acid-base indicator.
2. In the presence of an acid, blue litmus paper turns red.
3. In the presence of a base, red litmus paper turns blue.

pH scale

1. pH scale is used to signify the strength of an acid or a base.
2. pH of 7 indicates a neutral substance.
3. pH greater than 7 indicates basic behavior.
4. pH less than 7 indicates acidic behavior.

Explanation for the correct option

Option D

1. pH value of 10 indicates basic behavior.
2. Basic substances turn the color of red litmus paper to blue.

Explanation of incorrect options

Option A

pH 2 indicates acidic behavior which will not turn red litmus paper blue.

Option B

pH 5 indicates acidic behavior which will not change red litmus paper blue.

Option C

pH 7 indicates neutral behavior which will not change red litmus paper blue.

Therefore option D is the correct option.