An inversion layer exists in air that is:

An inversion layer is a meteorological phenomenon where the typical temperature gradient in the atmosphere is inverted. Normally, air temperature decreases with altitude, allowing cooler air to be situated at the ground level and warmer air to sit above it. However, in an inversion layer, this pattern is reversed. The ground-level air is cooler compared to the warmer air that is positioned above. This phenomenon can have significant implications for aerial applications, as it can trap pollutants close to the ground and affect the dispersion of sprays or chemicals used in agricultural practices.

The option indicating that the air is coolest at ground level and warmer above accurately represents this atmospheric condition, highlighting why the inversion layer differs from the usual temperature profile. This concept is essential for understanding air stability and weather patterns that can impact aerial application practices.