Correct Option
The correct option is Temperature decreases with altitude.
Explanation
The atmosphere is divided into five distinct layers based on temperature variations. The Mesosphere is the third layer, extending approximately from 50 km to 80 km above the Earth's surface, situated between the Stratosphere and the Thermosphere.
Option Analysis
- It contains the ozone layer. is Incorrect: The ozone layer is primarily located in the Stratosphere (specifically the lower stratosphere), where it absorbs ultraviolet radiation from the sun.
- Temperature decreases with altitude. is Correct: In the Mesosphere, temperature decreases with increasing altitude. This occurs because the layer is heated from below by the Stratosphere (which is warm due to ozone) and there are fewer gas molecules to absorb solar radiation as altitude increases. The temperature drops to approximately -90°C to -100°C at the Mesopause, the upper boundary of this layer.
- It reflects radio waves. is Incorrect: The reflection of radio waves is a characteristic of the Ionosphere, which is an extension of the Thermosphere containing electrically charged particles (ions).
- It is the hottest layer. is Incorrect: The Mesosphere is the coldest layer of the atmosphere, not the hottest. The Thermosphere contains the highest temperatures due to the absorption of high-energy solar radiation.
Key Takeaway: The Mesosphere is characterized by a decrease in temperature with altitude, making it the coldest atmospheric layer. It is also the region where most meteors burn up upon entering the Earth's atmosphere.