The correct option is It is located between 80 and 400 km..
Explanation
The Ionosphere is a functional layer of the Earth's atmosphere defined by its electrical properties rather than temperature. It contains electrically charged particles (ions) created by the ionization of atmospheric gases by solar radiation. This layer plays a critical role in radio communication by reflecting radio waves back to Earth.
Detailed Analysis:
- It is located below the Stratosphere. is Incorrect: The Stratosphere extends up to an altitude of approximately 50 km. The Ionosphere begins at a higher altitude, above the Mesosphere.
- It is located between 80 and 400 km. is Correct: The Ionosphere is located between 80 km and 400 km above the Earth's surface. It largely overlaps with the Thermosphere.
- It is the coldest layer of the atmosphere. is Incorrect: The Mesosphere is the coldest layer of the atmosphere, with temperatures dropping to -100°C. The Ionosphere is situated primarily within the Thermosphere, where temperatures rise significantly with altitude due to the absorption of solar radiation.
- It contains no gases, only vacuum. is Incorrect: The Ionosphere is not a vacuum. It consists of gas atoms and molecules (such as nitrogen and oxygen) that have been ionized. While the air density is extremely low compared to the surface, matter is present.
Key Takeaway:
The Ionosphere is an electrically charged layer located between 80 and 400 km altitude, primarily within the Thermosphere, and is responsible for reflecting radio waves to facilitate long-distance communication.