What colour precipitate is produced when iron (III) ions react with sodium hydroxide solution?

When iron (III) ions react with sodium hydroxide solution, a brown precipitate is formed. This results from the formation of iron(III) hydroxide, which has the chemical formula Fe(OH)₃. In solution, iron (III) ions ((Fe^{3+})) react with hydroxide ions ((OH^-)) from the sodium hydroxide to create this insoluble compound.

The brown color of the precipitate is characteristic of iron(III) hydroxide and is an important identification feature in qualitative analysis. This reaction serves as a demonstration of how transition metal ions can create colored compounds, a significant concept in chemistry.

The other options do not represent the color of the precipitate formed with iron (III) ions and sodium hydroxide. For instance, a white precipitate typically indicates the formation of compounds like silver chloride or barium sulfate, while yellow or green precipitates are associated with different metal ions or specific reactions that do not involve iron(III) hydroxide. Thus, the formation of a brown precipitate is the defining characteristic of the reaction in question.