Ncert Exercises & Solutions

The correct order of the packing efficiency in different types of unit cells is-

1. Fcc < Bcc < Simple cubic

2. Fcc > Bcc > Simple cubic

3. Fcc < Bcc > Simple cubic

4. Bcc < Fcc > Simple cubic

HINT: The packing efficiency is the fraction of the crystal (or unit cell) actually occupied by the atoms. FCC have highest packing fraction.

Explanation:

Packing efficiency in different types of unit cells can be tabulated as :

Unit cell

Packing efficiency

Fcc

Bcc

Simple cubic

74%

68%

52%

Hence, correct orderis Fcc (74%) > Bcc (68%) > Simple cubic (62%).