Magnesium oxide (MgO) has the rock salt crystal structure and a density of 3.58 g/cm³. The atomic weights of magnesium and oxygen are 24.31 g/mol and 16.00 g/mol, respectively.

(a) Determine the unit cell edge length.

nm

(b) Determine the unit cell edge length from the radii in the table below assuming that the Mg²⁺ and O^2- ions just touch each other along the edges.

nm

Cation		Ionic Radius (nm)		Anion		Ionic Radius (nm)
Mg2+		0.072		Cl-		0.181
Fe2+		0.077		O2-		0.140
Na+		0.102