Question

A student took four test-tubes I, II, III and IV containing aluminium sulphate, copper sulphate, ferrous sulphate and zinc sulphate solutions respectively. He placed iron strips in each one of them. After some time, he found a brown deposit formed in test-tube marked :

(1) I
(2) II
(3) III
(4) IV

Answer 1

In test tube II, iron is more reactive than copper, so it will displace copper from the copper sulphate solution. Due to this displacement reaction colour of solution changes from blue to green. The iron nail gets brown colour due to deposition of copper metal on its surface.
$\underset{\left(\mathrm{Grey}\right)}{\mathrm{Fe}}\left(\mathrm{s}\right)+\underset{\left(\mathrm{Blue}\right)}{{\mathrm{CuSO}}_4}\left(\mathrm{aq}\right)\to \underset{\left(\mathrm{Green}\right)}{{\mathrm{FeSO}}_4}\left(\mathrm{aq}\right)+\underset{\left(\mathrm{Brown}\right)}{\mathrm{Cu}}\left(\mathrm{s}\right)$

Hence, the correct answer is option 2.