Litmus is a common indicator which is used to identify acid and base. The colour of litmus paper turns to blue indicates that the chemical is a base. If there is no change in colour, then the chemical is either acidic or neutral.

(i) First of all, put the red litmus paper in each test tube one by one. In one of the test tube, the red litmus paper will turn blue which indicates the solution of that test tube is basic.

(ii) Now, put the blue litmus paper, formed above, in the remaining two test tubes. The solution which turns the blue litmus to red will be acidic.

(iii) The solution which does not change colour of any litmus paper will be neutral. Hence, it will be distilled water.