The unit cell in a certain lattice consists of a cube formed by an anion at each corner, an anion in the center, and a cation at the center of each face. The unit cell contains a net:

Answer 1

Corner atoms count as 1/8 each (only 1/8 of them is inside the boundaries of the unit cell)

Center/Body atoms count as 1 whole (whole thing inside the unit cell)

Face atoms count as 1/2 each (they're half in, half outside the unit cell)

(FYI edge atoms count as 1/4)

So for anions, the calculation is

1/8 anion at each corner x 8 corners on a cube = 1 anion

+ 1 whole anion

= 2 anions per cell

For cations, the calculation is

1/2 cation at each face x 6 faces on a cube = 3 cations per cell

The unit cell contains a net 3 cations and 2 anions.