Final answer:
The correct option is A. The layer of the atmosphere from 12 km to 50 km where little convection occurs is the stratosphere, characterized by a temperature increase with altitude due to UV radiation absorption by ozone.
Step-by-step explanation:
The region of the atmosphere you're asking about is known as the stratosphere. This layer extends from about 12 km to about 50 km above Earth's surface. Within the stratosphere, there is little convection taking place.
Unlike the troposphere, which lies below the stratosphere and where air temperature generally decreases with altitude and convection currents create weather, the stratosphere is characterized by a temperature increase with altitude due to the absorption of UV radiation by ozone. Additionally, the stratosphere is mostly free of clouds and contains the ozone layer, which protects us from harmful UV radiation.