Calculating Rf Value in Chromatography

Steps:

• Measure the distance from the baseline to the solvent front (total solvent travel).
• Measure the distance from the baseline to the center of each spot.
• Calculate Rf for each spot using the formula: Rf = (spot distance) / (solvent distance).
• Identify the spot where Rf = 0.75.

Why C is correct:

• Spot C's distance ratio yields exactly 0.75, matching the Rf formula definition as the relative mobility of the compound.

Why the others are wrong:

• A: Rf is lower (e.g., 0.4), as spot A travels less than 75% of solvent distance.
• B: Rf is around 0.6, not reaching 0.75 based on its position.
• D: Rf exceeds 0.75 (e.g., 0.9), indicating faster travel relative to solvent.

Final answer: C