Pick the incorrect environmental statement (BOD/COD, engine NOx, stratospheric profile, greenhouse effect) From the options below, identify the statement that is wrong based on fundamental environmental engineering principles.
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ABiological oxygen demand (B.O.D.) value of a sewerage sample is always lower than its chemical oxygen demand (C.O.D.) value.
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BEnvironmental pollution by NOx emission is much higher by four stroke petrol engines as compared to the two stroke engines.
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CTemperature in stratosphere rises with increasing altitude.
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DThe characteristic of a green house body is that it allows the long wavelength incoming solar radiation to come in but does not allow the short wavelength infra red radiation to escape out of the earth's atmosphere.
Answer
Correct Answer: The characteristic of a green house body is that it allows the long wavelength incoming solar radiation to come in but does not allow the short wavelength infra red radiation to escape out of the earth's atmosphere.
Explanation
Introduction / Context:Several staple facts in environmental engineering are tested here: the BOD–COD relationship, NOx propensity of engine cycles, vertical temperature structure of the stratosphere, and the physical basis of the greenhouse effect. One statement is deliberately reversed and must be identified as incorrect.
Given Data / Assumptions:
- BOD measures biodegradable organic load; COD measures total chemically oxidisable matter.
- Four-stroke spark-ignition engines typically have higher combustion temperatures and can produce more NOx than two-stroke counterparts (which tend to emit more HC and CO).
- Stratosphere exhibits a temperature inversion; temperature increases with altitude due to ozone absorption of UV.
- Greenhouse effect involves shortwave solar input and longwave terrestrial re-radiation.
Concept / Approach:Check each statement against fundamentals. The greenhouse statement is inverted: the atmosphere (and greenhouses) readily transmit shortwave solar radiation and restrict the escape of longwave infrared radiation emitted by the Earth’s surface.
Step-by-Step Solution:
(a) BOD < COD: Correct (biodegradable fraction is part of chemically oxidisable load).(b) 4-stroke vs 2-stroke NOx: Plausible/commonly true due to higher in-cylinder temperatures and better scavenging control in 4-strokes.(c) Stratospheric temperature profile: Correct (temperature rises with altitude).(d) Greenhouse statement: Wrong; it should read “allows shortwave solar radiation in and impedes longwave infrared out.”Verification / Alternative check:Textbook radiative balance and atmospheric profiles confirm (c); standard wastewater texts confirm BOD < COD; emission characterization of SI engines aligns with (b).
Why Other Options Are Wrong:
Only option (d) is incorrect; (a), (b), and (c) are consistent with fundamentals.Common Pitfalls:Mixing up “shortwave in” and “longwave out” in greenhouse descriptions; it is a frequent exam trick.
Final Answer:The characteristic of a green house body is that it allows the long wavelength incoming solar radiation to come in but does not allow the short wavelength infra red radiation to escape out of the earth's atmosphere.