Once the chromatographic column has been prepared, why is it important to allow the level of the liquid in the column to drop the level of the alumina before applying the solution of the compound to be separated?

Chromatography is a technique which is used for the separation of components present in a mixture into sub-components.

Explanation:

The solvent or liquid used for the separation of the chromatographic mixture should lie below the spot point where the mixture is loaded in an alumina column. This is done to prevent the air bubbles formations, which can lead to poor sanitation. Also this is done to prevent the mixing of the mixture to be separated with the solvent instead of running with the solvent via capillary action.