Litmus, was formerly prepared only in Holland, but at present is manufactured from various lichens in Italy, France and Britain. A peculiar blue coloring matter obtained from Roccella tinctoria, Acharius, and other lichens. Roccella tinctoria, or Orchilla weed, is a small, dry lichen, with a rounded, glaucous, nearly erect thallus, forked and subdivided into numerous branchy, roundish, gray, yellowish, or brownish threads; the apothecia are scattered, red and elevated; the disks are flat, caesius, pruinose, and as broad as the border.

Sulphur dioxide is produced during combustion of fossil fuels, refining of petroleum and smelting of sulphur containing ores. Sulphur dioxide produces smog and acid rain. Sulphur dioxide causes membrane damage, destruction of chlorophyll, necrosis and water soaked appearance. Lichens are the most sensitive organisms to sulphur dioxide pollution and do not grow in areas with high levels of sulphur dioxides. Hence Lichens like Usnea are used as indicators of level of sulphur dioxide pollution.

Lichens are sensitive to air pollution and hence they are absent in polluted areas. An extensive grwth of lichens indicate that the location is unpolluted.

Lichens are very sensitive to sulphur dioxide pollution in the air and hence they don't grow in polluted areas. They are found in unpolluted areas.

Litmus is got naturally from different species of Lichens. It is used as pH indicator to check the acidity of a material.

In perfumery, two species of lichen are used, namely Evernia prunastri and Pseudevernia furfuracea. These are commonly called as oakmoss and treemoss respectively. Evernia prunastri is found on oak trees. 

Competition present between the members of the same species compete for limited resources is called Intraspecific competitions. Intraspecific competition is affected not only by the type of competition but also by the type of resource. .

Lichens are mutualistic associations of a fungus and an alga or cyanobacterium and occur as crusty patches or bushy growths on trees, rocks and bare ground. 

Crustose lichen forms a thin crust growing on or in the substrate, and which cannot be detached from it. They may be areolate (divided into islands by cracks in the thallus). An upper cortex protects the algal layer in the medulla beneath, and there is often a differently coloured ring of actively growing fungal hyphae round the margin (the prothallus). Graphis is a crustose lichen.

Lichens are known as pioneer species, these can survive in places where higher plants finds it difficult to grow. Irrespective of the type of region, extremes in environmental conditions, mountainous terrains and high latitudes, lichens are good survivors. Besides these, the major ecological importance of the lichens are that these are poikilohydric. With little control over the status of hydration, these are able to tolerate irregular and even severe dessication. Thus, the correct answer is option C.

Parmelia is a genus of the family Parmeliaceae is a medium to large foliose lichens. These grow in a wide range of shapes and forms and is usually determined by the organization of the fungal filaments. The vegetative body is called as the thallus which helps in absorbing water. The route from lichen to alcohol was first via a treatment with acid to transform lichenin (a carbohydrate) into glucose and during the Second World War, there was industrial production of sugar from lichens in Russia. The incentive to use lichens came from the scarcity of beet sugar and the need to use grain or potato starch for military alcohol production. 

Lichens are mutualistic associations of a fungus and an alga or cyanobacterium. Lichens are very sensitive to sulphur dioxide pollution in the air. Lichens are sensitive to sulphur dioxide because their efficient absorption systems result in rapid accumulation of sulphur when exposed to high levels of sulphur dioxide pollution. The algal partner are most affected by the sulphur dioxide; chlorophyll is destroyed and photosynthesis is inhibited. Lichens also absorb sulphur dioxide dissolved in water. 

Lichens are mutualistic associations of a fungus and an alga or cyanobacterium and occur as crusty patches or bushy growths on trees, rocks and bare ground. Lichens are very sensitive to sulphur dioxide pollution in the air. Their efficient absorption systems result in rapid accumulation of sulphur when exposed to high levels of sulphur dioxide pollution. The algal partner is most affected by the sulphur dioxide; chlorophyll is destroyed and photosynthesis is inhibited. Lichens are widely used as environmental indicators or bio-indicators. If air is very badly polluted with sulphur dioxide, there may be no lichens present, just green algae may be found. If the air is clean, shrubby, hairy and leafy lichens become abundant. Thus, the correct answer is option A.

Lichens are most sensitive to sulphur dioxide pollution and do not grow in areas with high levels of air pollution. Hence, Lichens are an important indicators of air pollution.