Write a short note on litmus paper.

Litmus is extracted from lichens. It is most commonly used as an indicator to determine the chemical nature of substance. It has mauve or purple colour in distilled water. When it is added to an acidic solution, it turns red and when added to a basic solution, it turns blue. It is available in the form of a solution, or in the form of strips of paper, known as litmus paper. Generally, it is available as red and blue litmus paper.