The correct answer is: D. Lichen
Litmus is an indicator that is used to test the acidity or alkalinity of a solution. It is a mixture of two dyes, orcein and erythrol, which are extracted from lichens. Lichens are a symbiotic relationship between a fungus and an alga or cyanobacterium. The fungus provides the alga or cyanobacterium with a place to live and protection from the environment, while the alga or cyanobacterium provides the fungus with food.
Litmus is a natural product that has been used for centuries. It was first used in ancient Greece and Rome to test the acidity of wine. In the Middle Ages, it was used to test the acidity of urine to diagnose diseases. Today, litmus is used in a variety of applications, including chemistry, biology, and medicine.
Litmus paper is a type of litmus that is made into a paper. It is used to test the acidity or alkalinity of a solution by dipping the paper into the solution. The color of the paper will change depending on the pH of the solution. A blue litmus paper will turn red in an acidic solution, and a red litmus paper will turn blue in an alkaline solution.
Litmus is a valuable tool for scientists and other professionals who need to test the acidity or alkalinity of solutions. It is a simple and inexpensive way to get accurate results.