Using column chromatography, mixture of two compounds 'A' and 'B' was separated. 'A' eluted first, this indicates 'B'…

Step 1: Understand the Setup

In column chromatography:

• A polar adsorbent (silica gel or alumina) is the stationary phase
• A liquid solvent is the mobile phase
• Compound A eluted first → it spends less time on the column
• Compound B eluted second → it is retained longer on the column

Step 2: Relate Elution Order to Adsorption Strength

Compound that elutes first (A):

• Has weaker adsorption on the stationary phase
• Has higher $R_f$ value (moves more with the solvent)

Compound that elutes second (B):

• Has stronger adsorption on the stationary phase
• Has lower $R_f$ value (moves less with the solvent)

Step 3: Determine Properties of Compound B

Since B elutes after A:

• B has stronger adsorption on the adsorbent → B is more polar
• B has lower $R_f$ than A

Step 4: Evaluate Options

| Option | $R_f$ | Adsorption | Correct? | |---|---|---|---| | (a) | Low | Weaker | ❌ — contradiction (low $R_f$ means stronger adsorption) | | (b) | High | Stronger | ❌ — contradiction (high $R_f$ means weaker adsorption) | | (c) | High | Weaker | ❌ — B has low $R_f$, not high | | (d) | Low | Stronger | ✅ — consistent with B eluting after A |

Answer: (d) Low $R_f$, stronger adsorption

Key Points to Remember:

• Elutes first = weaker adsorption = higher $R_f$ (less polar compound)
• Elutes last = stronger adsorption = lower $R_f$ (more polar compound)
• $R_f$ and adsorption strength are inversely related on a polar adsorbent
• This relationship is fundamental to understanding both TLC and column chromatography