For the brown ring test, the correct order of the steps in the experi…

The correct answer is Option (1) → B, D, C, A

The brown ring test for nitrate is done on a solution of the salt. Ferrous sulphate is added first, and the concentrated acid last, so that it forms a separate layer at the bottom.

• B (first) — take half a spatula of the given salt in a dry test tube.

• D (second) — dissolve it in water to make a solution of the salt.

• C (third) — add 2–3 mL of freshly prepared ferrous sulphate solution.

• A (last) — pour a few drops of concentrated \( \ce{H2SO4} \) slowly along the side of the tube. Being dense, the acid forms a separate layer at the bottom, and a brown ring appears at the junction of the two layers.

\( \ce{Fe^2+} \) reduces nitrate to NO, which joins \( \ce{Fe^2+} \) to give the brown complex:

    \( \displaystyle \ce{NO3^- + 3Fe^2+ + 4H+ -> NO + 3Fe^3+ + 2H2O} \)

    \( \displaystyle \ce{[Fe(H2O)6]^2+ + NO ->} \underset{\text{brown}}{\ce{[Fe(H2O)5(NO)]^2+}} \ce{+ H2O} \)

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Brown Ring Test – “The familiar brown ring test for nitrates depends on the ability of Fe²⁺ to reduce nitrates to nitric oxide, which reacts with Fe²⁺ to form a brown coloured complex. The test is usually carried out by adding dilute ferrous sulphate solution to an aqueous solution containing nitrate ion, and then carefully adding concentrated sulphuric acid along the sides of the test tube. A brown ring at the interface between the solution and sulphuric acid layers indicate the presence of nitrate ion in solution.”