Which of the following is indicator of air pollution ?

The correct answer is C) Lichen. Lichens are the classic bioindicator of air quality. A lichen is a symbiotic partnership of a fungus and an alga or cyanobacterium. It has no root system and no protective waxy cuticle, so it takes in water and nutrients directly from the air and rain. That makes it highly vulnerable to sulphur dioxide and fluoride. Where SO2 levels are high, lichens die off first, and cities often show 'lichen deserts' near industrial zones.

• A) Puffballs: These are fungi that act as decomposers. They are not used as pollution indicators.
• B) Algae: Algal blooms indicate nutrient pollution in water bodies, through eutrophication. They are not air-pollution indicators.
• D) Moss: Mosses are also used in biomonitoring, especially for heavy metal deposition. But the standard textbook indicator for air pollution, especially SO2, is lichen, and the question expects that answer.

The concept links to Environment and Ecology, and to Mains questions on urban air quality and NCAP monitoring. Biological indicators complement instrument-based monitoring.

Trap: Aspirants pick moss because it is also a bioindicator. Remember that the standard answer for air pollution is lichen.