Which layer of the earth's atmosphere contains the ozone layer?

Which layer of the earth's atmosphere contains the ozone layer?

or

Which layer of the atmosphere contains the ozone layer?

Options:
1) Troposphere
2) Mesosphere
3) Ionosphere
4) Stratosphere
Answer: Stratosphere

The Earths atmosphere layers are similar to the layers in the interior of the Earth. The stratosphere contains a layer of relatively high concentrations of ozone.
The stratosphere is a layer of Earth's atmosphere. It is the second layer of the atmosphere as you go upward. The troposphere, the lowest layer, is right below the stratosphere. The next higher layer above the stratosphere is the mesosphere.
The ozone layer is mainly found in the lower portion of the stratosphere from approximately 20 to 30 kilometres (12 to 19 mi) above the earth, though the thickness varies seasonally and geographically.