What is chromatography?

Chromatography is fundamentally defined as a technique used to separate mixtures of colored compounds, which is precisely what the correct answer states. The primary principle behind chromatography is based on the differential affinities of components in a mixture for a stationary phase and a mobile phase. These differences in how compounds interact with these phases lead to separation as the mixture moves through the chromatographic system.

In practice, this technique is widely used in various fields such as chemistry, biology, and environmental science, to analyze and purify substances. For example, in paper chromatography, the mixture moves up the paper, and different substances travel at different rates due to their varying solubilities, leading to distinct bands of color.

Other options provided do not accurately define chromatography. Measuring concentrations is related to analytical chemistry methods but does not involve the separation aspect central to chromatography. The creation of chemical reactions is more aligned with synthesis techniques, while the mixing of solvents may be a preparatory step in some chromatography setups but does not represent the core function of the technique itself.