A solution contains nitrite ions. Explain the test that would be used to confirm the presence of the NO2- ions in solution. A solution contains nitrite ions. Explain the test that would be used to confirm the presence of the NO2- ions in solution. Solution 1.Start with adding dilute HCl or H 2 SO 4 in the solution. If you are able to see brown fumes. Then it may be Nitrite and fumes are due to evolution of NO which reacts with atmospheric oxygen to give brown fumes of NO 2 . 2. To the solution add a pinch of FeSO4 and then conc. H2SO4 from the side of the test tube, if it give a violet/brown ring at the junction, then it is nitrite. .