A piece of copper weighs $0.635g.$How many atoms of copper does it contain?

Question

$\begin{array}{1 1} (A)\;6.02\times 10^{21} \\(B)\;7.03\times 10^{22} \\(C)\;2.03\times 10^{21} \\ (D)\;6.02\times 10^{17} \end{array}$