1. The problem statement, all variables and given/known data CsCl has a BCC unit cell containing 2 atoms, Cs in the origin of the cell and Cl at the centre of the cell. Describe the CsCl unit cell in terms of its primitive cell+basis. 2. Relevant equations R = n1a1 + n2a2 + n3a3 ~ R is the vector which relates one point of the lattice to any other. 3. The attempt at a solution R = n1a1 + n2a2 + n3a3, Where Cs is at the point (0,0,0) and Cl is at the point (1/2,1/2,1/2) My issue is mostly with the terminology - I am not really sure what the question is asking. I know that either ion can be described with a SC lattice and together they make a BCC lattice. I don't really know how to answer this.