Answer. Ozone gas is found in stratosphere. Stratosphere region lies above the troposphere region and covers from 12 to 50 km of the atmosphere. It is considered that in the middle of the stratosphere formation of ozone takes place by the combination of oxygen molecule and atomic oxygen such as.
O2 + O ————> O3
Hence, formation of ozone in this region results in formation of ozone layer. Thus ozone layer exists about 25km to 30km away from the Earth's surface.