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

Litmus is extracted from lichens. It has a mauve (purple) colour in distilled water. When added to an acidic solution, it turns red and when added to a basic solution, it turns blue. So, it is used to test the acidic or basic nature of solutions.

https://www.tiwariacademy.com/ncert-solutions/class-7/science/chapter-5/