When healthy, earth's stratosphere contains a low concentration of ozone (O3) that absorbs potentially harmful ultraviolet (UV) radiations by the cycle shown below: O3 --(hv)-- O2 + O O2 + O --(Heat)

Question

When healthy, earth's stratosphere contains a low concentration of ozone (O3) 
that absorbs potentially harmful ultraviolet (UV) radiations by the cycle shown 
below:
O3 --(hv)--> O2 + O
O2 + O --(Heat)--> O3
chlorofluoro carbon refrigerants, such as freon 12 (CF2Cl2), are stable in lower
atmosphere, but in the stratosphere, they absorb high energy UV radiation to 
generate chlorine radicals.
CF2Cl2 --hv--> CF2Cl• + Cl•
The presence of small number of chlorine radicals appears to lower ozone 
concentrations dramatically. The following reactions are all known to be 
exothermic (except the one requiring light) and to have high rate constant.
A : Cl—O—O—Cl --hv--> O2 + 2Cl•
B : Cl—O• + O -> O2 + Cl•
C : Cl• + O3 -> Cl—O• + O2
D : 2Cl—O• -> Cl—O—O—Cl

Prashant Kotian · Accepted Answer

Correct answer: A. Step 1: Understand that the biosphere is the region of the Earth that contains living organisms and where these organisms interact. Step 2: Option (a) describes the biosphere as the zone in which individuals interact with one another and with their physical environment. Step 3: Therefore, option (a) is the correct definition of the biosphere.

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