How many unit cells are present in a cubic shaped ideal crystals of NaCl of mass 1.0g?

Question

$\begin{array}{1,1}(a)\;1.28\times10^{21} unit\;cells\\(b)\;1.71\times10^{21} unit\;cells\\(c)\;2.57\times10^{21} unit\;cells\\(d)\;5.14\times10^{21} unit\;cells \end {array}$