What is the color of Fe^3+ (aq) ion?

The correct answer is Option (1) → Yellow

The colour of a transition metal ion in solution comes from d–d transitions: an electron in a lower d orbital absorbs visible light and moves to a higher one, and we see the complementary colour of the light absorbed. Ions with an empty (d⁰) or full (d¹⁰) d subshell cannot do this and are colourless.

Fe (Z = 26) is \( \mathrm{[Ar]\,3d^{6}\,4s^{2}} \); losing the two 4s electrons and one 3d electron gives \( \ce{Fe^3+} \): \( \mathrm{3d^{5}} \). The hydrated \( \ce{Fe^3+} \) ion is yellow (for comparison, \( \ce{Fe^2+} \), 3d⁶, is green).

NCERT (2026-27 edition):
Formation of Coloured Ions – …