You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?

Hint: By the use of litmus paper, we can find the character of a given solution, that is, whether it is acidic or basic. Acid converts blue litmus paper into red and base converts red litmus paper into blue.

Complete step by step solution:
In the question, we are provided with three different solutions in three test tubes. One of the solutions contains distilled water meaning that it is neutral and the other two are acidic and basic solutions. We know that acid solution turns litmus red, base turns it blue and neutral solution does not cause any change in the colour of the litmus paper. We are given the question that we have been provided only with red litmus paper.
So we add a few drops of each of the three solutions separately on the litmus paper.
The solution which changes the colour of the red litmus paper to blue is the basic solution. Since acid solution turns litmus to red colour there will be no change in the colour of red litmus paper.We have identified the basic solution and have two solutions left.
Now, we use the litmus paper that was turned blue by the base to find out the acidic solution. The solution which turns the blue litmus paper to red will be the acidic solution, while the one that changes the colour of neither the red nor the blue litmus paper, is the neutral solution or distilled water.

Note:
Litmus is extracted from different dyes of lichens. It is soluble in water and is adsorbed on filter papers to form the litmus paper used to test the pH of solutions.