Q.Describe the major source of air pollution.

Lichens are the textbook bio-indicator of SO2 pollution, making option (d) the correct pairing among the four.

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Certain plants and plant-like organisms are used as biological indicators of specific air pollutants because they show visible damage (chlorosis, necrosis, reduced growth, or local disappearance) at pollutant concentrations too low to be obvious by other means. For sulphur dioxide (SO2), the single most widely cited bio-indicator is the lichen -- a symbiotic association of a fungus and an alga/cyanobacterium. Lichens lack a waxy cuticle and absorb gases (including SO2) directly over their whole surface, and their photosynthetic algal partner is especially sensitive to sulphite toxicity; as a result, lichens are killed or fail to establish in areas with even modest SO2 pollution, and the sharp fall in lichen diversity around industrial/urban centres (sometimes called a 'lichen desert') is a classic, long-used indicator of chronic SO2 pollution. Sensitive flowering ornamentals such as rose have also been used in pollution-monitoring gardens as visible SO2-sensitive indicator plants alongside lichens. Checking the other options: Gladiolus is more specifically known as an indicator of fluoride pollution; Petunia and Chrysanthemum are more specifically associated with sensitivity to ozone/PAN (photochemical smog) rather than SO2; and Robinia pseudoacacia and Casuarina are nitrogen-fixing trees valued for soil improvement and windbreaks, not classic SO2 bio-indicators. Of the four pairs, only (d), which includes lichens, correctly names the standard SO2 indicator.

Acid rain is caused by air pollution, specifically when certain gases released into the atmosphere mix with rainwater.

A scrubber is an air-pollution control device that removes both particulate matter (dust) and gaseous pollutants from industrial exhaust before it is released.

A scrubber works by passing polluted exhaust gas through a spray or bed of a scrubbing liquid (often water or an alkaline solution). Fine dust and particulate matter are trapped/washed out by the liquid droplets, while acidic or other soluble gaseous pollutants (such as SO2) are absorbed and neutralised by chemical reaction with the scrubbing liquid. Because it removes both solid and gaseous pollutants in one unit, it is distinct from devices like electrostatic precipitators or cyclone separators, which mainly remove only particulate matter.

Part (a): Air pollution causes respiratory diseases (asthma, bronchitis, lung cancer) and heart problems, plus eye and throat irritation.

Part (b): Noise pollution causes hearing loss and deafness and raises stress, disturbing sleep and causing high blood pressure and poor concentration.

Photochemical smog is a mixture of secondary pollutants — PAN, ozone, and NO2 — formed by sunlight-driven reactions of primary pollutants.

Note on scope: this question tests air-pollution chemistry (photochemical smog), part of the 'Environmental Issues' unit. That specific unit is not part of the current rationalised NCERT syllabus this platform's chapter content is built from, so a chapter-linked lesson isn't available here — but the question itself has a clear, well-established answer, given below.

Photochemical smog forms when primary pollutants from vehicle/industrial exhaust — nitrogen oxides and unburnt hydrocarbons — react with each other in the presence of sunlight (UV radiation), producing a cocktail of secondary pollutants. Its major components include:

• PAN (peroxyacetyl nitrate) — a strong eye and respiratory irritant.
• Ozone (O3) — formed by photolysis of NO2 and reaction of NO with hydrocarbon free radicals.
• Nitrogen dioxide (NO2) — and other oxidants such as formaldehyde.

All three are simultaneously present in photochemical smog, so the correct choice is 'All of the above'.

PUC checks keep vehicle emissions within legal limits, curbing air pollution and its health effects.

Vehicles burning petrol or diesel release polluting gases such as carbon monoxide, unburnt hydrocarbons, oxides of nitrogen, and particulate matter, all of which degrade air quality and contribute to respiratory diseases, smog formation and global warming. A PUC (Pollution Under Control) certificate is issued only after a vehicle's exhaust emissions are tested and found to be within government-prescribed limits. Making this mandatory for all vehicles ensures that poorly maintained or high-polluting vehicles are identified, repaired or taken off the road, thereby reducing the overall vehicular contribution to urban air pollution, safeguarding public health, and helping cities meet air-quality standards.