The correct answer is option 2: Partition.

In paper chromatography, a mixture of different substances is separated into its individual components using a chromatographic technique. The principle behind this process is based on the concept of partition. Partition refers to the distribution of a substance between two immiscible phases, which in this case is the mobile phase (solvent) and the stationary phase (paper).

During paper chromatography, a paper strip is used as the stationary phase. The mixture to be separated is spotted onto the paper and the lower end of the paper is placed in a solvent, which acts as the mobile phase. The solvent ascends the paper through capillary action, carrying the mixture components with it.

As the solvent moves up the paper strip, the individual components of the mixture interact differently with the stationary phase and the mobile phase. The interactions between the mixture components and the stationary phase cause them to separate, resulting in distinct bands or spots on the paper strip.

The separation of the mixture components occurs because each component has a different level of affinity for both the stationary phase and the mobile phase. This variation in affinity leads to differential partitioning of the components, allowing for their separation based on their chemical properties.

Therefore, the principle involved in paper chromatography is partition,