Rf Value and Fe(OH)₃ Precipitate Color in Chromatography

Steps:

• Rf value is the ratio of distance traveled by the Fe³⁺ spot to the solvent front distance.
• Spraying with NaOH forms Fe(OH)₃ precipitate at the starting line, making the Fe³⁺ spot visible.
• The chromatogram shows Fe³⁺ spot at position x, so Rf corresponds to x.
• Fe(OH)₃ precipitate is red-brown, confirming the color for the Fe³⁺ identification.

Why A is correct:

• Fe(OH)₃ forms a red-brown precipitate with NaOH, and x marks the Fe³⁺ spot position per standard chromatography results.

Why the others are wrong:

• B: Green color is incorrect; Fe(OH)₃ is red-brown, not green (which might indicate Fe²⁺).
• C: Duplicate of A, but if distinct, assumes wrong spot position; x is correct for Fe³⁺.
• D: y position is wrong for Fe³⁺ spot, and green is incorrect color.

Final answer: A