Which layer is the uppermost atmospheric layer where temperature increases with altitude?

• A. Troposphere
• B. Stratosphere
• C. Thermosphere
• D. Mesosphere

Answer: (C)

In this question, the behavior of temperature with height in Earth's atmosphere is key. The uppermost layer where temperature rises as you go higher is the thermosphere. This happens because the few gas molecules here absorb high-energy solar radiation (like UV and X-rays). That energy heating increases the average kinetic energy of those particles, so the temperature climbs with altitude. Even though the air is extremely thin, so it would feel cold to us, the measured temperature can be very high because it reflects how energetically the particles are moving. Below this layer, temperature trends differ: the troposphere generally cools with height, the stratosphere warms with height due to ozone absorption, and the mesosphere cools with height. Since the thermosphere is the outermost layer and it gets hotter with altitude, it’s the correct one for this description.