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Environment & Ecology question from JKAS Prelims, 2018 by JKPSC

Which of the following statement(s) is/are true?

 i) In Stratosphere, Ozone is formed by joining oxygen atom with oxygen molecule in presence of solar radiation
ii) The disassociation of oxygen atom in the presence of solar radiation maintains the balance of Ozone in the Stratosphere
 iii) The maximum concentration of Ozone is around 23-25 km from the Earth’s surface
 iv) The destruction of Stratospheric ozone by green house gases has reduced considerably during last 5 years due to the Montreal Protocol.

Last updated May 30, 2026
Correct Answer: Option B — i,ii and iii are correct
Detailed Analysis of the Statements
Statement (i) is TRUE: Stratospheric ozone is formed naturally through the Chapman Mechanism. High-energy solar ultraviolet (UV-C) radiation splits an oxygen molecule ($O_2$) into two free oxygen atoms ($O$). A free oxygen atom then combines with an unbroken $O_2$ molecule in the presence of solar radiation to form ozone (O_3).
Statement (ii) is TRUE: The balance of the ozone layer is maintained by a continuous cycle of creation and destruction. Ozone molecules absorb UV radiation and dissociate back into an oxygen molecule ($O_2$) and a free oxygen atom ($O$). This continuous cycle is called the Ozone-Oxygen Cycle.
Statement (iii) is TRUE: While the ozone layer spans roughly from 10 to 50 km above Earth, its highest concentration (the peak thickness of the layer) is found in the lower stratosphere, precisely around 23–25 km (often generalized as 20–30 km) above the Earth's surface.
Statement (iv) is FALSE: The Montreal Protocol targets Ozone-Depleting Substances (ODSs) like Chlorofluorocarbons (CFCs), Hydrochlorofluorocarbons (HCFCs), and halons—not greenhouse gases in general (though some ODSs are also potent greenhouse gases). While the protocol has successfully set the ozone layer on a path to recovery, statement (iv) incorrectly attributes ozone destruction fundamentally to greenhouse gases.
Answer verified by Quintessence Classes faculty — Karan Nagar, Srinagar.
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JKPSC JKAS 2018 Prelims

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Exam JKPSC
Recruitment JKAS
Stage Prelims
Year 2018
Subject Environment & Ecology
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