Question

i. Why do lichens do not occur in delhi whereas they commonly grow in manali or darjeeling ii. Lichens r called pioneer colonisely of base rocks. How can they help in d formation of soil?

Answer 1

Here are the main reasons ,for what lichens do not occurs in Delhi.
(1):- In Delhi, the air is very much polluted with different gases, sulphur dioxide is one of them, released by various industries, Lichens are sensitive to sulphur dioxide,so when they interact with air for moisture absorption, they get affected by sulphur dioxide (2):- The amount of rainfall is very low in Delhi, result is less amount of water vapour in atmosphere,

But in case of Manali , Darjeeling,  the amount of rainfall is quite high which favours the growth of Lichens.
Lichens are the organisms that are formed by the association of the filamentous fungus and the microscopic green algae or Cyrano bacteria. Fungus provides moisture, minerals to algae and in turn algae provides food through the process of photosynthesis.

Answer 2

Delhi is polluted but Darjeeling and Manali are not polluted