In the simple cubic unit cell, the centers of identical particles define the of a cube.

Answer is: In the simple cubic unit cell, the centers of  eight identical particles identical particles define the corners of a cube.
There is three types of cubic cell:
1) simple cubic unit cell.
2) body-centered cubic unit cell.
3) face-centered cubic-unit cell.
The simple cubic unit cell is the simplest repeating unit in a simple cubic structure, the edge of a unit cell always connects equivalent points.

Cr(oh)3 -> cr(3+) + 3oh-

Idk the answer sorry