Concept:Chromatography is a physical separation method based on differential distribution between stationary and mobile phases.
It cannot separate isotopes because isotopes have nearly identical chemical properties and thus behave identically in chromatographic processes.
Explanation:Isotopes of the same element have the same electronic configuration and chemical reactivity.
Chromatography relies on differences in affinity, solubility, or adsorption, which do not vary between isotopes.
Thus, techniques like diffusion, distillation, centrifugation, thermal diffusion, exchange reactions, or electrolysis are used for isotope separation, not chromatography.
In contrast, chromatography can separate colours from a dye, pigments from natural colour, and drugs from blood because these have distinct chemical structures and interact differently with the stationary and mobile phases.
Answer:Option A: radio‑isotopes.