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.

Question

Quizplus · Accepted Answer

The statement that the faces of a unit cell must all be at angles of 90° to each other is incorrect because this only describes cubic unit cells. Other types of unit cells, such as tetragonal, orthorhombic, hexagonal, rhombohedral, monoclinic, and triclinic, can have angles that are not 90°.

Which One of the Following Statements About Unit Cells and Packing