"Green Muffler" is related to

Concept: In environmental engineering, a dense, multi-row belt of trees and shrubs planted along a noisy corridor (a highway, an industrial estate, or an engine-testing area) works as an acoustic barrier — the foliage absorbs and scatters sound waves before they reach nearby residents, so such plantation schemes are classified under noise-pollution abatement measures.

Application: The 'Green Muffler' scheme applies exactly this principle. Multiple rows (typically four to six) of dense, broad-leaved trees and shrubs such as Neem, Peepal, and Ashoka are grown around residential colonies, industrial units, highways, and engine-testing zones. Their thick canopy intercepts and dampens the sound generated by traffic and machinery before it reaches the surrounding population — the word 'muffler' itself names a sound-suppressing device, which is exactly the function this green belt performs. This is the primary, standard classification tested by this question, and it matches the keyed answer, Noise pollution.

• Soil pollution — soil contamination results from chemicals, plastics, or waste seeping into land; a roadside tree belt does not remediate soil quality, so this is unrelated.

• Air pollution — the same foliage does secondarily trap some dust and absorb certain gases (this is a genuine, textbook-noted co-benefit), but it is not the defining, name-giving function of the scheme, which centers on sound dampening.

• Water pollution — this concerns contamination of rivers, lakes, or groundwater; a land-based plantation scheme has no direct role in treating water bodies.

Cross-check: This question has appeared across multiple competitive exams with the same four options. Most exams (including this one) key it uniquely to Noise pollution, matching the standard textbook definition of Green Muffler as a noise-absorbing belt. Note for awareness: at least one exam's answer key controversy (MPPSC State Services 2023, upheld by the Madhya Pradesh High Court in May 2024) additionally credited Air pollution as correct, citing a textbook passage noting the same belt also absorbs pollutant gases — but that was a dispute specific to that exam's key; the standard and here-keyed answer remains Noise pollution.

Result: 'Green Muffler' is therefore correctly classified under noise pollution control.