Which of the following is indicator of air pollution?

1. A

   Puffballs

   Puffballs are fungi whose fruiting bodies release spores; they are not the standard bioindicator of urban air quality in this syllabus list. Lichens, not puffballs, are the classic SO2-sensitive markers. This option names the wrong fungus group.

2. B

   Algae

   Algae are used more as water-quality and eutrophication indicators than as the textbook air-pollution indicator among these four. Some aerophytic algae exist, but the keyed air indicator here is lichen. Algae miss the standard pairing.

3. C

   Lichen

   (c) Official key: Lichens (symbiosis of fungus and alga/cyanobacterium) are highly sensitive to sulphur dioxide and other air pollutants; their absence or species composition indicates air quality. They are the classic biological indicator of air pollution in Indian prelims. Among puffballs, algae, lichen and moss, lichen is keyed.

4. D

   Moss

   Mosses can indicate moisture and some pollution stress, but the standard one-word air-pollution indicator in this set is lichen. Moss is a distractor from bryophyte ecology. The keyed choice remains lichen.

Summary. Official key is (c). Lichens are sensitive to air pollutants, especially SO2, and are used as bioindicators of air quality. Puffballs are not used that way in this question; algae point mainly to water; mosses are a weaker distractor. The indicator to mark is lichen.