The correct option is A SO2
Lichens are compound organisms, that shows symbiotic relationship between fungus and photosynthetic organism (algae). It is varies in size, colors and forms. It appears as cranky patches or fluffy growth on rocks, trees and exposed ground. Lichens are very sensitive to SO2
pollution in the air, therefore it can be represented as air pollution signals. This is because their productive consumption structure results in speedy aggregation of sulphur when resolved to high levels of sulphur dioxide pollution. One of the partner in lichens (photosynthetic organism) shows to be greater damaged by sulphur dioxide; and thereby causes photosynthesis to be inhibited and chlorophyll is destroyed.
So, the correct answer is option A.