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$\degree$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 faces of a unit cell do not necessarily have to be at 90 degree angles to each other. In fact, there are many crystals with non-rectangular unit cells, such as hexagonal crystals.

Which One of the Following Statements About Unit Cells and Packing