$CuSO_4$ solution(250ml) was electrolysed using a platinum anode and a copper cathode.At constant current of 2mA was passed for 16 minutes.It was found that after electrolysis the absorbance of this solution was reduced to 50% of its original value.Then the concentration of copper sulphate in solution to begin with is

Question

$\begin{array}{1 1}(a)\;8\times 10^{-4}\\(b)\;8\times 10^{-5}\\(c)\;8\times 10^{-6}\\(d)\;8\times 10^{-7}\end{array}$