1. What is a unit cell in crystal structures? 2. Calculate the Atomic Packing Factor, APF, for a Body-Centered Cubic, BCC, structure. Assuming atoms are hard spheres, the Atomic Pack Factor for a given crystal structure can be expressed as: APF=VolumeofunitcellVolumeofatomsinunitcell Show your work. 3. What is the theoretical density of silver, Ag at 20C. Show your work. why do you think there is a difference between the theoretical density and the typical density value experimentally measured, 10.49g/cm3 ? 4. What does it mean when we say a certain property of a material is anisotropic? Explain in the context of the elastic constant of single crystal BCC iron. Also, in a macroscale sample made out of this single crystal BCC iron, what does it mean? 5. For the two unit cells below: (b) a. What are the indices for the directions indicated by the two vectors in sketch (a)? b. What are the indices for the two planes drawn in sketch (b)