The correct option is A Iron (Fe)
CuSO4 solution is blue in colour due to the presence of copper ion Cu2+. To see a colour change, Cu should be displaced from this solution.
We know that to displace a metal (in this case, copper Cu2+ from its salt solution CuSO4), we need a metal which is more reactive than Cu.
Gold and lead are less reactive than copper and cannot displace it. Iron Fe on the other hand is more reactive than Cuand hence can displace Cu from its salt solution to form ferrous sulphate which is green in colour.