KI crystallizes in a cubic unit cell with I- ions on each corner and each face

Answer here: https://biology-forums.com/index.php?topic=290161.0

Follow the same approach as below


4 k+ and 4 Br- are present in each unit cell.

Total corner in one cubic unit cell = 8

1 atom on unit cell is shared by 8 unit cell. So 1/8 of the atom is present in each unit cell

So total atom in unit cell at corner , 8 × 1/8 = 1

Atom present on face is shared by two unit cell.

Total face in simple cubic unit cell = 6

So total atom in each unit cell = 6×12 = 3

When atom is present on all corners and all faces, this arrangement is call face centered cubic (FCC)unit cell.

So total Br- = 1 (from all corner) + 3(from all faces) = 4

So we can say that KBr crystallizes in FCC.

So there are 4 K+ and 4 Br- ions are present in each unit cell