In paper chromatography, why is a lid placed on top of the container?

In paper chromatography, placing a lid on top of the container serves the essential purpose of preventing the solvent from evaporating. When the solvent evaporates, it can lead to a change in concentration and could potentially affect the results of the chromatography. If the concentration of the solvent decreases due to evaporation, the movement of the ink or pigment on the chromatogram may become erratic, leading to inaccurate separation of the components.

The other options do not address the primary function of the lid in this context. While the absorption of ink may be affected by other factors, the lid's primary role is not to facilitate absorption. Light exposure and temperature maintenance are also important factors in some experiments, but these are not the main reasons for using a lid in chromatography. The evaporation of the solvent is the most immediate concern that the lid addresses, ensuring consistent and reliable results.