Which One of the Following Statements About Unit Cells and Packing

Multiple Choice

Which one of the following statements about unit cells and packing in solids is incorrect?

A) In any unit cell of a solid crystal, each face of the cell must have an opposite face which is equal and parallel to it.
B) The faces of a unit cell must all be at angles of 90° to each other.
C) The coordination number of atoms in a close packed metal is 12.
D) The packing efficiency in fcc structures is higher than in bcc structures.
E) The packing efficiency in fcc and hcp structures is the same.