It protects us from harmful sun rays.
Explanation
The ozone layer is a specific region within the Earth's atmosphere containing a relatively high concentration of ozone ($O_3$). It plays a vital role in maintaining the biosphere by filtering solar radiation.Analysis of Options:
- It is located in the Mesosphere. is Incorrect: The ozone layer is primarily located in the Stratosphere, approximately 15 to 35 kilometers above the Earth's surface. The Mesosphere lies above the Stratosphere.
- It traps heat to keep the earth warm. is Incorrect: The process of trapping heat to keep the Earth warm is the Greenhouse Effect, which is primarily driven by gases such as carbon dioxide ($CO_2$), methane ($CH_4$), and water vapor in the Troposphere. While ozone absorption does heat the Stratosphere, its primary definition in this context is not the retention of surface heat.
- It protects us from harmful sun rays. is Correct: The ozone layer absorbs the majority (about 97-99%) of the Sun's medium-frequency Ultraviolet (UV) light (specifically UV-B and UV-C), which is harmful to living organisms.
- It is the most plentiful gas in the atmosphere. is Incorrect: Ozone is a trace gas. The most plentiful gas in the atmosphere is Nitrogen (constituting roughly 78%), followed by Oxygen (21%).
Key Takeaway: The Ozone Layer is situated in the Stratosphere and serves as a protective shield against harmful Ultraviolet (UV) radiation.