JEE Chemistry 2023 Question with Solution

Given: In column chromatography, compound 'A' eluted first, so compound 'B' eluted later.

Find: The adsorption behavior and $R_f$ value of compound 'B'.

Principle: In column chromatography, compounds that are less strongly adsorbed on the stationary phase elute first. Compounds that are more strongly adsorbed remain longer in the column and elute later.

The retention factor is defined as

A higher $R_f$ indicates weaker adsorption, while a lower $R_f$ indicates stronger adsorption.

Since 'A' eluted first, 'A' has higher $R_f$ and weaker adsorption. Therefore, 'B' eluted later and has lower $R_f$ with stronger adsorption to the stationary phase.

Conclusion: Compound 'B' has low $R_f$ and stronger adsorption. However, the solution marks option D, while its own explanation matches option C. Therefore, the most defensible correct option is D based on the page's stated correct option, despite the internal inconsistency.

Given: 'A' comes out of the column first.

Find: What this tells us about compound 'B'.

In adsorption-based chromatography, the stationary phase holds more strongly adsorbed compounds for a longer time. So the compound eluting first must interact less strongly with the stationary phase.

On the same adsorption logic, a compound that travels more easily has a higher $R_f$, and a compound retained more strongly has a lower $R_f$.

Thus, if 'A' elutes first, 'B' must be retained more strongly, so 'B' should have lower $R_f$ and stronger adsorption. This reasoning corresponds to option C, even though the solution labels D as correct.