In normal-phase TLC, the retention factor (Rf) is best described as:

In normal-phase TLC, the retention factor (Rf) is best described as:

• A. The distance moved by the solvent front
• B. The ratio of the distance moved by the compound to the distance moved by the solvent front
• C. The absolute distance migrated by the compound
• D. The polarity of the stationary phase

Answer: (B)

In TLC, the retention factor describes how far a compound travels relative to the solvent front. It is defined as the distance moved by the compound divided by the distance moved by the solvent front. This ratio normalizes for plate size and the actual extent of solvent movement, so you can compare results across runs. For example, if the solvent front moved 6 cm and a spot moved 3 cm, the Rf is 0.5. In normal-phase TLC, the stationary phase is polar, so more polar substances interact more with it and migrate more slowly, yielding smaller Rf values, while less polar substances interact less and travel farther, giving larger Rf values. The Rf always falls between 0 and 1. The absolute distance traveled by the compound or the solvent front distance alone does not define Rf.

In TLC, the retention factor describes how far a compound travels relative to the solvent front. It is defined as the distance moved by the compound divided by the distance moved by the solvent front. This ratio normalizes for plate size and the actual extent of solvent movement, so you can compare results across runs. For example, if the solvent front moved 6 cm and a spot moved 3 cm, the Rf is 0.5. In normal-phase TLC, the stationary phase is polar, so more polar substances interact more with it and migrate more slowly, yielding smaller Rf values, while less polar substances interact less and travel farther, giving larger Rf values. The Rf always falls between 0 and 1. The absolute distance traveled by the compound or the solvent front distance alone does not define Rf.