Which of the following is most suitable indicator of SO2 pollution in the environment?

Lichens show the symbiotic relationship of fungus and algae. Lichens are plants that develop in uncovered places such as rock or tree bark. They are very perceptive to sulphur dioxide (SO2) pollution in the air. Therefore, they are widely accepted as environmental indicators or bio-indicators. That is, if the air is clean, they can be understood that SO2 is less in the atmosphere and this results in the bushy, hairy and leafy lichens can be found. Whereas, if the air contains abundant SO2 there may be no lichens present. So, the correct answer is option B.