The atomic weight of Cu is 63.546.There are only two naturally occuring isotopes of copper,$^{63}Cu$ and $^{65}Cu$.The relative abundance of the $^{63}Cu$ isotope must be

Question

$\begin{array}{1 1}(a)\;11.3\% \\ (b)\;31.5\% \\(c)\;52.4\% \\(d)\;72.7\% \end{array}$