a 4. (10%) Magnesium has an HCP crystal structure, with a c/a ratio of 1.624, and a density of 1.74 g/cm. Compute the atomic radius for Mg. 5. (10%) Niobium has an atomic radius of 0.1430 nm and a density of 8.57 g/cm3. Determine whether it has an FCC or BCC crystal structure. 6. (10%) Titanium (Ti) has an HCP crystal structure and a density of 4.51 g/cm a) What is the volume of its unit cell in cubic meters? b) if the c/a ratio is 1.58, compute the values of c and a