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 soution respectively . If you are given only red litmus paper, how will you identify the contents of each test tube?

Explanation

First of all, we will put one strip of red litmus paper in each test tube. In one of the test tubes, the litmus paper will turn blue. It is sure that this test tube contains basic solution. The remaining two test tubes contain distilled water and acidic solution in both of which red litmus remains red.
Now, we will pour out some basic solution from the test tube, so that only a little amount remains in it. Then, we will pour the contents of one of the remaining test tubes into the test tube containing basic solution. Two things may happen.
(i) The litmus -may turn red again : This indicates that the second test tube contains acidic substance. And the other one contains distilled water.
(ii) The litmus may remain blue : This indicates that he poured liquid is distilled water. And the other one is the acidic solution.