Estimate the Density of Magnesium Oxide from Its Crystal Structure

Estimate the density of magnesium oxide from its crystal structure.The radii of Mg²⁺ and O^{2 -} are 72 and 140 pm,respectively.

A) 3.51 g.cm ^{- 3}
B) 14.9 g.cm ^{- 3}
C) 21.1 g.cm ^{- 3}
D) 1.76 g.cm ^{- 3}
E) 0.878 g.cm ^{- 3}