Identifying the Fe(aq) spot via precipitate color in chromatography

Steps:

• Spray the chromatogram with NaOH to visualize ions by forming colored hydroxide precipitates.
• Fe³⁺(aq) forms a red-brown precipitate of Fe(OH)₃ at its spot position (noting possible query error on "iron(II)").
• Measure Rf as distance from origin to this red-brown precipitate spot divided by solvent front distance.
• In the diagram, this red-brown spot is in row x, completing the gaps for Rf and color.

Why A is correct:

• Red-brown precipitate specifically identifies Fe³⁺ per standard qualitative analysis, matching row x in the result diagram.

Why the others are wrong:

• B: y position does not correspond to the Fe spot location.
• C: Duplicate of A; not distinct.
• D: Green precipitate indicates Fe²⁺ or another ion (e.g., Ni²⁺), not Fe(aq) here, and y is incorrect position.

Final answer: A