Task: Class Definition Understanding (ontology: Earth_Environment/SWEET)

Which of the following definitions best describes 'free instability'?

A. An instability due to the buoyancy force of heavy fluid over light fluid overcoming the stabilizing influence of viscous forces.
B. The ability of a fluid at rest to become turbulent or laminar due to the effects of buoyancy.
C. The state of a layer of unsaturated air when its lapse rate of temperature is less than the dry-adiabatic lapse rate but greater than the moist-adiabatic lapse rate.
D. An instability of the basic flow of an incompressible inviscid fluid in two parallel infinite streams of different velocities and densities.

Answer: The state of a layer of unsaturated air when its lapse rate of temperature is less than the dry-adiabatic lapse rate but greater than the moist-adiabatic lapse rate.