Question

Read the following statements.
a) Ozone is found mostly in the stratosphere.
b) The Ozone layer lies $55 - 75kms$ above the surface of the earth.
c) Ozone absorbs ultraviolet radiation from the sun.
d) Ozone layer has no significance for life on the earth.
Which set of the statements is correct?
A) $a$ and $c$
B) $b$ and $d$
C) $b$ and $c$
D) $a$ and $d$

Answer 1

Hint: The relative concentration of ozone molecules in the atmosphere is low. There are usually a few thousand molecules per billion air molecules in the stratosphere at the maximum concentration level of the ozone layer.
The energy of these ultraviolet high-energy rays in our atmosphere is so great that they are completely absorbed by our stratosphere. When even low-energy radiation is absorbed by an ozone molecule, it is separated into an ordinary oxygen molecule and a free oxygen atom.

Complete solution:
The bulk of ozone (approximately $90\% $) is present in the Stratosphere, starting roughly $10 - 16$ kilometres over the surface of the Earth, stretching up to a height of around $50$ kilometres. The stratosphere with the largest concentration of ozone is generally referred to as the ozone layer. The altitude and width of the ozone layer spreads across the entire globe. In the troposphere, the residual ozone, about $10\% $, is contained between the Earth's crust and stratosphere, the lowest area of the atmosphere.
Thus we can say that the ozone layer lies mostly in the stratosphere.
Sun radiation is absorbed by the UV-B. In case of UV-B absorption of an ozone molecule, the oxygen molecule and the oxygen atom are isolated. Later the ozone molecule can be reformed from all elements. The UV-B-absorption of the stratosphere stops the ozone layer from touching the Earth's atmosphere at dangerous amounts of this radiation.
Thus we conclude that ozone absorbs the ultraviolet radiations emitted from the sun.

Therefore, the correct option is A.

Note: One can assume that all the ozone molecules in our troposphere and stratosphere are being carried back to the earth’s surface to evenly disperse those molecules to a cloud of gas expanding across the globe.
The use of nitric oxide, chlorine, hydroxyl and Bromine will also degrade ozone through catalytic photochemical reactions. CFCs are moving in here. CFCs drift into the stratosphere and separate into the cluster and cluster. This then speeds up the ozone breakdown.