Which compound is the least polar compound in a mixture analyzed by thin-layer chromatography (TLC)?

• A. The compound that remains at the baseline
• B. The compound with the highest $Rf$ value
• C. The compound with the lowest $Rf$ value
• D. The compound that travels the shortest distance up the plate

Answer: (B)

Verified step by step guidance

1. Understand that in thin-layer chromatography (TLC), polarity plays a key role in how far a compound travels on the plate. The stationary phase (usually silica gel) is polar, and the mobile phase is less polar.
2. Recall that polar compounds interact strongly with the polar stationary phase, causing them to move more slowly and travel a shorter distance up the plate.
3. Nonpolar (least polar) compounds interact less with the stationary phase and are carried further by the mobile phase, resulting in a higher distance traveled.
4. The retention factor, \(\mathrm{R_f}\), is defined as \(\mathrm{R_f} = \frac{\text{distance traveled by compound}}{\text{distance traveled by solvent front}}\).
5. Therefore, the compound with the highest \(\mathrm{R_f}\) value travels the farthest and is the least polar compound in the mixture.