The correct statements among the following, for a "chromatography" purification method is:

Step 1: Analyse Statement (a)

"Organic compounds run faster than solvent in TLC" ❌

False. By definition, $R_f < 1$ always. The solvent front travels faster than any compound. If a compound moved at the same speed as the solvent, it would have $R_f = 1$ — meaning zero adsorption. In practice, compounds always interact with the adsorbent to some extent, so $R_f$ is always less than 1.

Step 2: Analyse Statement (b)

"Non-polar compounds are retained at top; polar compounds come down in column chromatography" ❌

False — this is the exact opposite of reality. On a polar adsorbent (silica gel/alumina):

• Polar compounds → stronger adsorption → move SLOWLY → retained higher up in the column
• Non-polar compounds → weak adsorption → move FAST → elute first (exit at the bottom)

Step 3: Analyse Statement (c)

"$R_f$ of a polar compound is smaller than that of a non-polar compound" ✅

True. On polar adsorbents (silica gel, alumina):

• Polar compound → stronger adsorption → shorter distance traveled → lower $R_f$
• Non-polar compound → weaker adsorption → longer distance traveled → higher $R_f$ $R_f(\text{polar}) < R_f(\text{non-polar})$

Step 4: Analyse Statement (d)

"$R_f$ is an integral value" ❌

False. $R_f$ is always a decimal fraction strictly between 0 and 1 (e.g., 0.4, 0.7, 0.82). It is never a whole number.

Conclusion: Only statement (c) is correct → Option (c)

Key Points to Remember:

• $R_f$ range: 0 to 1 (decimal, never > 1, never an integer)
• Solvent front always moves faster than any compound in TLC
• Polar compound → stronger adsorption → lower $R_f$ → retained longer in column
• Non-polar compound → weaker adsorption → higher $R_f$ → elutes first