Aqueous solution of Mohr’s salt gives a positive test for:

Ferrous, ammonium and sulphate ions

The correct answer is (d) Ferrous, ammonium and sulphate ions. Mohr's salt is a double salt of ferrous ammonium sulphate. It contains ferrous ions, ammonium ions, and sulphate ions. Therefore, an aqueous solution of Mohr's salt will give a positive test for all three ions.

Ammonium ions can be tested for by adding a few drops of Nessler's reagent to the solution. If the solution turns brown, then it contains ammonium ions. Sulphate ions can be tested for by adding a few drops of barium chloride solution to the solution. If the solution turns white, then it contains sulphate ions. Ferrous ions can be tested for by adding a few drops of potassium thiocyanate solution to the solution. If the solution turns red, then it contains ferrous ions.