Adsorption is a surface phenomenon where molecules of a substance, such as a gas or a liquid, accumulate on the surface of another material, usually a solid. Let’s analyze each option to see which one cannot be explained by adsorption:

Option A: When acetic acid solution is shaken with charcoal, the concentration of acid decreases.

This can be explained by adsorption because acetic acid molecules adhere to the surface of the charcoal, reducing their concentration in the solution.

Option B: The white precipitate of Mg(OH)₂ attains a blue color when precipitated in the presence of magneson reagent.

This can be explained by adsorption because the magneson reagent might adsorb onto the surface of Mg(OH)₂, imparting a blue color to it.

Option C: An aqueous solution of NaOH attains pink color with a drop of phenolphthalein.

This cannot be explained by adsorption. The pink color is due to a chemical reaction where phenolphthalein acts as a pH indicator in a basic solution, turning pink at pH levels above 8.3. This is a chemical property of phenolphthalein rather than adsorption.

Option D: When animal charcoal is shaken with colored methylene blue solution, the solution turns colorless.

This can be explained by adsorption because the methylene blue molecules adsorb onto the surface of the charcoal, removing the color from the solution.

Of all the options, Option C cannot be explained by adsorption because it involves a chemical reaction indicating the presence of a base.

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Surface Chemistry · Chemistry · BITSAT

MCQ (Single Correct Answer)