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UPSC Prelims 1987 · Environment · Pollution Files
Ozone layer of atmosphere absorbs
- (a) Ultraviolet rays
- (b) Infrared rays
- (c) All radiations of light
- (d) Cosmic rays
Show the answer and explanation
Answer: (a) Ultraviolet rays
The ozone layer absorbs most of the harmful ultraviolet radiation.
The idea
Ozone is made and destroyed by ultraviolet light itself. UV splits an oxygen molecule; a free oxygen atom joins another O₂ to make ozone (O₃); ozone then absorbs UV and splits again. In this cycle the energy of UV is turned into heat and never reaches the ground.
UV splits O₂ into two oxygen atoms → O + O₂ → O₃ (ozone) → Ozone absorbs UV and splits → UV energy becomes heat → So the stratosphere gets warmer with height
Why the others are wrong
(b) Infrared is absorbed by greenhouse gases like CO₂ and water vapour.
(c) Visible light passes through.
Elimination technique
Option (c) says “all radiations of light”. Absolute words usually mark the wrong option in Environment PYQs.
Also know
About 90% of the atmosphere’s ozone is in the stratosphere, mostly between 15 and 35 km. Infrared is absorbed by carbon dioxide and water vapour, which is the greenhouse effect, a different story.
🔒 Ozone layer: 15–35 km, absorbs UV-B and UV-C.