Q1. London Smog (1952) was:
a) Industrial
b) Classical
c) Volcanic
d) Photochemical
Answer: (b) Classical
Explanation :
• Triggered by SO₂ + soot + stagnant cold air, forming sulphurous reducing smog—not photochemical (which requires NOx + sunlight).
• Visibility dropped to <5 m; >12,000 excess deaths documented.
• Similar conditions seen during 2025 Delhi winter, when high SO₂ + PM₂.₅ under temperature inversion produced reducing-type smog (CPCB AQI > 500 in some pockets).
Q2. High BOD indicates:
a) Thermal pollution
b) Heavy metal contamination
c) Organic pollution
d) High dissolved oxygen
Answer: (c) Organic pollution
Explanation :
• Biochemical Oxygen Demand (BOD) measures oxygen required by microbes to break down organic matter.
• Higher BOD → greater microbial respiration → lower DO → anoxic conditions.
• Example: Yamuna (2025) recorded 45 mg/L BOD in Delhi stretch (CPCB NAMIS), classifying it as “septic”; organic load from untreated sewage is the major cause.
Q3. Correct order in an aquatic food chain (DDT accumulation):
1.Zooplankton
2.Phytoplankton
3.Large fish
4.Small fish
a) 2 → 1 → 3 → 4
b) 3 → 1 → 2 → 4
c) 4 → 3 → 2 → 1
d) 2 → 1 → 4 → 3
Answer: (d) 2 → 1 → 4 → 3s
(Phytoplankton → Zooplankton → Small fish → Large fish)
Explanation :
• Bioaccumulation begins in phytoplankton (low trophic level).
• Biomagnification intensifies up the chain because DDT is lipophilic, persistent, non-metabolizable.
• 2025 WII Ganga Dolphin Survey showed elevated DDT in apex predators, confirming continued legacy pesticide movement in food webs.
Q4. CPCB day-time residential limit:
a) 75 dB
b) 45 dB
c) 55 dB
d) 65 dB
Answer: (c) 55 dB
Explanation :
• CPCB’s Noise Pollution (Regulation & Control) Rules, 2000 specify 55 dB (day) and 45 dB (night) for residential zones.
• Exceedances cause hypertension, sleep disturbance, cognitive decline (WHO).
• 2025 Delhi Metro Phase-4 construction faced NGT action for exceeding 75–80 dB, breaching limits by >20 dB.
Q5. Chernobyl & Fukushima: common failure?
a) Human error
b) Cooling failure
c) Tsunami
d) Core meltdown
Answer: (d) Core meltdown
Explanation :
• Chernobyl (1986): design flaw + operator error → uncontrolled reaction → explosive core meltdown.
• Fukushima (2011): tsunami disabled power → cooling failure → hydrogen explosion → core meltdowns in Units 1–3.
• 2025 IAEA status review highlights continuing waste containment challenges; contrasts with India’s Tarapur & Kudankulam, where passive safety systems prevent meltdown scenarios.
