12. Magnesium (Mg) has an HCP crystal structure, and a density of 1.74g/cm". Molar mass of Mg = 24.31g/mol. 1 pm = 1 x 10-10 cm. (a) (8 points) What is the volume of its unit cell in cm? (b) (8 points) If the c/a ratio is 1.623, compute the values of cand a. (unit: pm) (c) (4 points) Compute the atomic radius for Mg (unit: pm). (d) (2 points) The coordination number of Mg in this crystal is Page 6 of 16