On reaction of sodium hydroxide with Iron(II) ion gives the coloured precipitate. Tell the colour:
(A) Dark green
(B) Pink
(C) Red
(D) White

Hint: Iron is ductile, malleable and lustrous metal. It is the metal with four different crystalline forms. The rusting property of iron exists in damp air not in dry air. It has the ability to get dissolved in dilute acids.

Complete answer: Sodium hydroxide is known as caustic soda with the chemical formula of NaOH. It is soluble in water, glycerol and ethanol, but insoluble in ether and acetone. Iron being a transition metal form coloured compounds. If sodium hydroxide is added to the transition metal then the formation of transition metal hydroxide takes place. The formed hydroxide is insoluble so the formation of solid precipitate takes place. These precipitate appears as a suspended particle in solution. So if iron(II) is added to sodium hydroxide we get a dark green coloured precipitate. So the correct answer for this question is option ‘a’that is dark green coloured precipitate. The iron (II) ion is a ferrous iron which is pale green in colour, but in addition to water it changes to violet colour. It has the paramagnetic properties. But it can become diamagnetic on the formation of low spin complexes.

Hence the correct option is (A).

Note: The iron(III) ion forms orange brown precipitate on addition of sodium hydroxide solution. But on the addition of water it changes to a yellow brown colour. Iron is a good conductor of heat and electricity. Copper ion gives blue colour precipitate on addition of sodium hydroxide solution.