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

Litmus is a natural indicator. A natural Indicator is a type of indicator that can be found naturally and can help us to know whether the material tested is an acidic substance or a basic substance.

Some examples of natural indicators other than litmus are:  red cabbage, turmeric, turnip skin, curry powder, etc.

Litmus solution is extracted from lichens. Lichens are plants belonging to the Thallophyte group.

The process of obtaining a litmus solution needs the crushing and grinding of lichens.

These dyes are then added to neutral water to get the required litmus solution. It is often absorbed onto filter paper to produce one of the oldest forms of pH indicator known as Litmus paper. 

It is used to test materials for acidity and basicity. This solution can also be used to differentiate between acids and bases. When acid is added to a litmus solution, it changes to red. When a base is added, it changes to blue. Neutral litmus paper is purple in colour.