Question

___________ turns red litmus to blue.
A.Acid
B.Base
C.Salt
D.Water

Answer 1

Hint:Litmus paper is a pH paper made which is made by treating natural dyes from the lichens with the litmus. To perform a litmus test, we place a small drop of sample onto the litmus paper.

Complete step by step answer:
-We know that below 7.0 pH range, everything is considered to be acid and everything above 7.0 pH range is considered to be a base. 7.0 is the standard neutral pH range in the pH scale.
-When we dip a red litmus paper in a base solution, it turns red. When we dip a blue litmus paper in an acid solution, it turns red. So, we can say that acid turns red litmus to blue.
-Therefore, we can conclude that out of the given four options, A is the correct option. B, C and D are incorrect options.
Hence the correct option is A.

Additional information:
Litmus paper also has few limitations. It does not give value of the pH, it also does give a numerical form of pH value. It is just roughly determined if a sample is an acid or a base. Also, the paper can show change in colour for some other reasons too besides an acid-base reaction.
There are various limitations of pH. These are:
1)pH value is zero for \[{\text{1}}\,{\text{N}}\] solution of strong acid.
2)pH value is negative for concentrations of \[2\,{\text{N,}}\,{\text{3}}\,{\text{N}}\] ions of the strong acids.
3) Instead of pH, the Hammett acidity function is used at higher concentrations.

Note:
We must use a red litmus paper for testing a basic solution and a blue litmus paper for testing an acid solution. Solutions having pH below 7 are usually acids and above pH 7 are basic.