The coldest region of the atmosphere

The correct option is Mesosphere.

To understand why the mesosphere is the coldest region of Earth's atmosphere, we can analyze the temperature profile of the atmospheric layers from the ground up:

1. Troposphere: This is the lowest layer, extending up to about 12 km. Temperature decreases with altitude in this layer because it is heated by the Earth's surface.

2. Stratosphere: Extending from about 12 km to 50 km, the temperature increases with altitude in this layer due to the absorption of ultraviolet (UV) radiation by the ozone layer.

3. Mesosphere: Extending from about 50 km to 85 km, the temperature once again decreases with altitude. Because there are very few molecules (like ozone) to absorb solar radiation in this layer, and because carbon dioxide efficiently emits heat energy into space, temperatures drop dramatically. Near the top of the mesosphere (the mesopause), temperatures reach their absolute minimum in the entire atmosphere, falling as low as about -90°C (183 K or -130°F). This makes it the coldest layer of Earth's atmosphere.

4. Thermosphere: Extending above 85 km, the temperature rises rapidly with altitude due to the absorption of highly energetic solar radiation (X-rays and shortwave UV) by the extremely sparse gas molecules.

Consequently, the mesosphere is established as the coldest atmospheric region.