Ms. Neelam, a class 10 teacher took Cu, Al, Pb and Zn strips respectively in four test tubes labelled as, I, II, III and IV and added 10 mL of freshly prepared ferrous sulphate solution to each test tube as shown in the figure :

Black residue would be obtained in test tubes

Options

A. I and II only
B. I and III only
C. II and III only
D. II and IV only.

Answer

D

Explanation

Reactivity series of metals is :
`Al gt Zn gt Fe gt Pb gt Cu`
A more reactive metal displaces a less reactive metal from the solution of its salt.
thus, only Al and Zn displace Fe from ferrous sulphate solution.
`underset("Aluminium")(2Al) + undersetunderset("sulphate")("ferrous")(3FeSO_(4))toundersetunderset("sulphate")("Aluminium")(Al_(2)(SO_(4))_(3))+undersetunderset("(black residue)")("Iron")(3Fe)`
`underset("Zinc")(Zn) + underset("Ferrous sulphate")(FeSO_(4))to underset("Zinc sulphate")(ZnSO_(4))+undersetunderset(("Black residue"))("Iron")(Fe)`
Thus a black residue of Fe will be obtained in test tubes II and IV only.