Question

What is the coordination number of BCC and FCC crystal structures?

• A. $8$ and $8$
• B. $8$ and $10$
• C. $8$ and $12$
• D. $12$ and $12$

Answer 1

The correct option is C

$8$ and $12$

Explanation for the correct option:

(c ) $8$ and $12$

• The central atom of Body Centred Cubic crystal structure is in contact with the atoms on the 8 corners, thus, the coordination number of BCC is $8$
• The central atom of Face Centred Cubic crystal structure is in contact with the atoms on the 8 corners and on the 4 faces, thus the coordination number of the FCC crystal structure is $8+4=12$
• Hence this option is correct

Explanation for the incorrect options:

(a) $8$ and $8$

• BBC is $8$ and FCC is $12$
• this option states BBC to be $8$ and FCC to be$8$
• Thus, option (a) $8$ and $8$is incorrect.

(b)$8$ and $10$

• BBC is $8$ and FCC is $12$
• this option states BBC to be $8$ and FCC to be$10$
• Thus, option (b) $8$ and $10$ is incorrect.

(d) $12$ and $12$

• BBC is $8$ and FCC is $12$
• this option states BBC to be $12$ and FCC to be$12$
• Thus, option (d) $12$ and $12$ is incorrect.

Hence the correct option is (c ) $8$ and $12$