Paper chromatography is a technique used to separate mixtures and identify unknown substances. It works by partitioning components in a mixture between a stationary phase (paper) and a mobile phase (solvent). As the solvent travels up the paper, different components move at different rates depending on how strongly they bind to the paper. This causes the components to separate into distinct spots. The distance each spot travels allows it to be identified by its retention factor (Rf value). Paper chromatography is used in various applications such as environmental testing, forensic analysis, and quality control in manufacturing.