The thermosphere is the hottest layer because it

because there is not a lot of anything in that layer so anything that comes into it creates a reaction, heat

Explanation:

Because there are relatively few molecules and atoms in the thermosphere, even absorbing small amounts of solar energy can significantly increase the air temperature, making the thermosphere the hottest layer in the atmosphere"

because the light is a great source of energy for the plants to survive. (i hope this )

2%? i tried finding the exact sorry if it's not 100% correct ; -;