What is the layer of atmosphere present just above the earth's surface?

The order of the layers of the atmosphere from the earth's surface (moving away from the surface) is

Calculate the work required to raise a body of mass m to a height h just above the earth's surface. Radius of the earth is R and acceleration due to gravity at the earth's surface is g.

Deoes the atmospheric pressure vary with the height above the earth's surface?

Which atmospheric layer is closest to the Earth's surface?

Which layer of the earth's atmosphere reflect back the radio waves to the earth's surface?