Question

In which condition does blue litmus paper turn red?
A.Acidic
B.Basic
C.Neutral
D.None of these

Answer 1

Hint:
litmus paper is used to distinguish a particular solution to be either acid or base depending on the color to which it changes. Usually the red color denotes that the solution has a pH lesser than $7$ and blue denotes that it has a pH greater than $7$.

Complete step by step answer:
 litmus paper is an important lab apparatus that can be used to confirm whether a solution is in acidic condition or alkaline condition. There are two types of litmus paper. There is a red litmus paper and a blue litmus paper. The red litmus paper can turn to blue color when it comes in contact with an alkaline solution. This change denotes that the solution is indeed alkaline. The blue litmus on the other hand, turns red when it is dipped in an acidic solution. This denotes that the solution is acidic.
The reason why a litmus paper changes color is due to the fact that it contains a pigment known as flavin. This pigment is water soluble and is sensitive to pH changes. The hydrogen ions in the acidic solution can cause a shift to red color whereas the presence of hydroxide ions causes a shift to blue color. It is important to note that if a solution like chlorine is taken and a litmus paper is dipped into it due to the bleaching capacity of chlorine, the litmus paper can become colorless for that reason and we end up with a white litmus paper.
Therefore, the answer to the above question will be option A that is acidic condition.

Note: It is important to know that if a blue litmus paper is introduced to an alkaline solution it remains the same color. If a red litmus paper is introduced to an acidic solution it still remains the same color. Therefore, we have to use the litmus paper that is suitable to the conditions that are present.