Name the source from which litmus solution is obtained. What is the use of this solution?

Litmus is most commonly used natural indicator which is extracted from lichens*. Litmus solution has mauve (purple) colour in distilled water. It is used as an indicator to distinguish between acids and bases. When acidic solution is added in it, it turns red and when basic solution is added, it turns blue.

Lichen* is an organism that is obtained from algae.