Question

A student placed a clean iron nail in blue coloured copper sulphate solution for a considerable time. He observes that :
(1) iron nail gets green coating
(2) iron nail gets brown coating
(3) iron nail gets no coating
(4) iron nail gets blue coating

Answer 1

When a clean iron nail is placed in a blue coloured copper sulphate solution, it displaces the copper from copper sulphate being more reactive than copper. The displaced brown coloured copper gets deposited over the clean iron nail, and with time, it forms a brown coloured coating on the iron nail.
$\underset{\mathrm{Blue}}{{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)}+\underset{\mathrm{Grey}}{\mathrm{Fe}\left(\mathrm{s}\right)}\to \underset{\mathrm{Green}}{{\mathrm{FeSO}}_4\left(\mathrm{aq}\right)}+\underset{\mathrm{Brown}}{\mathrm{Cu}\left(\mathrm{s}\right)}$

Hence, the correct answer is option 2.