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A student takes Cu, Al, Fe and Zn pieces separately in four test tubes labelled as I, II, III, and IV respectively. He adds 10 mL of freshly prepared ferrous sulphate solution to each test tube and observes the colour of the metal residue in each case.
He would observe a black residue in the test tubes :
(1) (I) and (II)
(2) (I) and (III)
(3) (II) and (III)
(4) (II) and (IV)"
Correct answer: (4) (II) and (IV)
Explanation: Case(1) Copper is reactive than iron hence, no reaction takes place.
Case (I1) When iron sulphate is added to aluminium, aluminium sulphate is formed and iron is deposited in the test tube. So the green colour of FeSO4 disappears.
Case (I1I) When iron sulphate is added to iron, no change will be observed as both metal is same, i.e. iron.
Case (IV) When iron sulphate is added to the zinc, then zinc sulphate and iron are deposited in the test tube. Hence, the green colour of iron sulphate disappears.
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