What is the principle behind how paper chromatography separates mixtures?

The principle of paper chromatography relies on the different affinities of substances for the stationary phase (the paper) and the mobile phase (the solvent). When a mixture of substances is applied to the paper and a solvent is allowed to move up the paper, each component of the mixture interacts with the two phases to varying degrees.

Some substances may have a stronger attraction to the stationary phase, causing them to move more slowly, while others may interact more favorably with the mobile phase, allowing them to travel further up the paper. This differential movement results in the separation of the components based on their unique properties, such as polarity and solubility. Over time, this leads to distinct spots on the paper, each representing a different substance from the mixture.

The other options do not accurately describe the mechanisms of separation in paper chromatography. For instance, stating that all substances move at the same rate disregards the crux of why separation occurs in the first place. Similarly, the notions of evaporation at different temperatures and equal solubilization in the solvent are not relevant to the fundamental principle of chromatography, which fundamentally involves the differing attractions of substances to the two phases.