Question

Why lichens are called 'indicators of air pollution'?

Answer 1

lichens can b  used as industrial pollution indicators because they will not grow in areas that r polluted

Answer 2

Pollutants and toxic substances present In the air can hinder the natural growth of lichens and can also damage them. Specifically ( SO)2

Can damage the growth of lichens

For this reason lichens are called "indicators of air pollution ".