Potassium crystallizes in a body centred cubic lattice. What is the approximate number of unit cells in 4.0 g of potassium? Atomic mass of potassium = 39.

Question

$\begin{array}{1 1}(A)\;3.09\times 10^{22}&(B)\;3.09\times 10^{20}\\(C)\;3.09\times 10^{18}&(D)\;3.09\times 10^{-22}\end{array} $