Question

In the closest packing of atoms A (radius $=r_a)$, the radius of atom B that can be fitted into the tetrahedral voids is :

• A. $0.155r_a$
• B. $0.225r_a$
• C. $0.414r_a$
• D. $0.732r_a$

Answer 1

The correct option is B $0.225r_a$

In the closest packing of atoms A (radius $=r_a$), the radius of atom B that can be fitted into the tetrahedral voids is

0.225 $r_a$ or 0.414 $r_a$. For the tetrahedral void, the limiting value of radius ratio is in the range 0.225 to 0.414.

For planar triangular void, it is 0.155 to 0.225. For the octahedral void, it is 0.414 to 0.732.

So, the minimum possible radius possible is $0.225r_a$
Hence, the correct option is B.