"The arrangement of atoms or ions in a crystal " is described by the terms body-centered cubic and face-centered cubic.
Explanation:
Face centred cubic system explains the crystal structure where an atom is present at each cubic corner of the crystal and the centre of each cube face. Meaningfully, a closed packed plane where at each "face of the cube" atoms touch the alongside face diagonals.
Whereas in body centric cube system has the lattice point present at the 8 corners of cell and an additional one at the center of the cell. Thus, both explains how the atom or ions are placed or arranged in a crystal.
