How many spots are produced by a pure substance during paper chromatography?

In paper chromatography, a pure substance will produce one distinct spot on the chromatogram. This occurs because a pure substance consists of only one type of molecule, leading to a single, specific interaction with the chromatography paper and the solvent. As the solvent moves up the paper, it carries the pure substance with it, resulting in a spot that corresponds to that substance's specific mobility in the chosen solvent system.

The behavior of a pure substance is distinct from mixtures, which can produce multiple spots as different components have varying affinities for the stationary phase (the paper) and the mobile phase (the solvent). Each component in a mixture will migrate at its unique rate, creating multiple spots. Therefore, the one-spot outcome is a defining characteristic of a pure substance in chromatography.