Question

Which is the coldest and hottest layer of atmosphere??

Answer 1

Coldest layer of Earth's atmosphere is the MESOSPHERE.The temperature there is -90 degree celsius. It can even go lower.
Hottest layer of Earth's atmosphere is the thermosphere. The temperature can go upto 1,500 degree celsius as it is sensitive to The sun rays.

Answer 2

The coldest layer of atmosphere is Mesosphere, which is 88 km from stratosphere. At 88 km, the temperature is -100 degree celsius, which is the minimum temperature of atmosphere. Meager clouds known as Noctilucent  clouds are formed there.

The hottest layer of atmosphere is Thermosphere because it is adjacent to the sun and secondly presence of ions which are radical. At 350 km, the temperature is +1200 degree celsius which is highest temperature of atmosphere. Because of high temperature, all meteor and space shuttle burn in this layer.