The correct option is It reaches minus 100°C.
Explanation
The Earth's atmosphere is divided into distinct layers based on the vertical variation of temperature. The layer extending from the stratopause (approx. 50 km) to an altitude of 80 km is known as the Mesos.
Detailed Analysis:
- Temperature Trend: Within the Mesosphere, temperature decreases with an increase in altitude. This contrasts with the underlying Stratosphere, where temperature increases with height.
- The Mesopause: The upper boundary of the Mesosphere, located at approximately 80 km, is called the Mesopause.
- Minimum Temperature: At this height (80 km), the temperature reaches the lowest value found anywhere in the atmosphere, dropping to approximately minus 100°C.
- Transition: Above the Mesopause lies the Thermosphere (Ionosphere), where temperatures start rising rapidly due to the absorption of solar radiation.
Key Takeaway:
The Mesopause at 80 km altitude represents the coldest point in the Earth's atmosphere, with temperatures reaching approximately -100°C.