What happens to the speed of molecules in a cooling air column?

When an air column cools, the kinetic energy of the molecules within that column decreases. This occurs because temperature is a measure of the average kinetic energy of the molecules; as temperature drops, the molecules move slower. In practical terms, a cooling air column leads to fewer high-energy collisions among the air molecules, reflecting a reduction in their overall speed. Thus, as the air cools, the speed of the molecules decreases, aligning with the second choice provided.

In contrast, the other choices do not hold true for a cooling air column. An increase in speed would contradict the principle of kinetic energy and temperature correlation, and stating that the speed stays the same or varies with altitude implies stability or inconsistency that does not accurately apply to the synonymous relationship between temperature and molecular movement in this context.