Which statement best describes how a higher Rf value relates to polarity on a polar stationary phase?

• A. Higher Rf indicates the solute is more polar relative to the stationary phase.
• B. Higher Rf indicates the solute is less polar relative to the stationary phase.
• C. Rf values do not depend on polarity.
• D. Higher Rf indicates the solute is less polar relative to the stationary phase.

Answer: (D)

In TLC with a polar stationary phase, polarity determines how strongly a solute interacts with the stationary material versus how far it can travel with the mobile phase. Polar compounds bind more tightly to the polar stationary phase, so they migrate slowly and stay closer to the origin, giving small Rf values. Less polar (or nonpolar) compounds interact weakly with the stationary phase and travel farther with the moving solvent front, resulting in larger Rf values. So, a higher Rf means the solute is less polar relative to the stationary phase. The exact numbers depend on the solvent system, but the general trend holds: increasing polarity relative to the stationary phase lowers Rf, while decreasing polarity relative to the stationary phase raises Rf.