Which of the following cations will form an insoluble red-brown compound with [Fe(CN)6]4- ? — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Step 1: The reaction of metal ions with potassium ferrocyanide, K4[Fe(CN)6], yields characteristic colored precipitates. Step 2: Copper(II) ions (Cu2+) react with ferrocyanide ions ([Fe(CN)6]4-) to form a highly insoluble, chocolate-brown/red-brown precipitate of copper ferrocyanide, Cu2[Fe(CN)6]. Step 3: Therefore, the cation that forms the red-brown compound is Cu2+, matching option (c).