You have been provided with three test-tubes. One of these test-tubes contains distilled water and the other two contain an acidic and a basic solution respectively. If you are given only blue litmus paper, how will you identify the contents of each test- tube?
If the colour of blue litmus does not change, then it is alkali. If the colour of blue litmus changes to red, then it is base. If there is no change in the colour of blue litmus/red litmus then it is distilled water due to the absence of ions.