part b only please, thank you!

2. (a) Consider cubic close-packing of oxygen ions. What is the ratio of number of ions in octahedral sites to oxygen ions in a unit cell? What is the ratio of number of ions in tetrahedral sites to oxygen ions in a unit cell? (b) Explain what valence of cations are required to have stable structures in which: 1. All octahedral sites are filled. 2. All tetrahedral sites are filled. 3. Half the octahedral sites are filled. 4. Half the tetrahedral sites are filled. Give an example of each