Hint:Let us first understand what is meant by the atmospheric pollution indicator. Atmospheric pollutants include particulate matter, carbon dioxide, carbon monoxide, sulphur dioxide, nitrogen oxides etc. The substances that indicate the increase or decrease in the level of these pollutants are known as atmospheric pollution indicators.
Lichens are the living organisms that are composed of fungi that are in symbiotic association with algae or cyanobacteria. They occur in different kinds of environments that range from sea level to high alpine mountains. They are capable of growing on any surface and are usually found on rocks and bark of trees.
The rainwater contains the air pollutants specially sulphur dioxide which is hazardous to lichens and causes damage and prevents them from growing. Therefore in highly polluted areas, the lichens are absent and hence they act as the natural indicators of air pollution or atmospheric pollution.
Lepidoptera: they are the group of insects that includes moths and butterflies and are the most widespread insects in the world. They are distinct from other insects in having scales that are modified as flattened hairs that give butterflies and moths different colours.
Lycopersicon: they are the type of flowering plants that belong to the family Solanaceae. They include thirteen species of tomato group of nightshade plants. Wild tomatoes and potatoes are also included in this group.
Lycopodium: they are the group of club mosses and are commonly called ground pines or creeping cedars. They are the vascular, flowerless and epiphytic plants that have creeping stems with needle-like leaves. They are called club mosses because of the club shaped appearance of the stem.
Therefore the correct answer is option (B) Lichens.
Note:Lichens have the well-balanced symbiosis such that they are considered to have a self contained miniature ecosystem among themselves. Along with the air pollution indication, lichens are also used to assess ozone depletion and metal contamination. They are also used to make perfumes, dyes and some traditional medicine.