The brown ring test for NO3^- is due to the formation of the complex ion with formula: — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Step 1: During the brown ring test, nitrate is reduced to nitric oxide (NO) by iron(II) in an acidic medium. Step 2: The generated NO gas coordinates with unreacted hydrated Fe2+ ions in the aqueous layer to form a brown coordination complex. Step 3: The formula of this brown complex is [Fe(H2O)5(NO)]2+, corresponding to option (c).