Question

If radius of a metal atom $\left(A\right)$ is 5pm and radius of an electronegative atom $\left(B\right)$ is 20pm, then in the unit cell:

• A. $A$ in octahedral voids, $B$ in FCC unit
• B. $A$ in FCC unit, $B$ in tetrahedral void
• C. $A$ in BCC unit, $B$ in cubic void
• D. $A$ in tetrahedral void, $B$ in FCC unit

Answer 1

The correct option is D $A$ in tetrahedral void, $B$ in FCC unit

Here, radius of $B$ is larger than $A$ so, $A$ is must be in void.

Now,

$\frac{r^{+}}{r^{-}}=\frac{5}{20}=0.25,$ which is tetrahedral

Hence, the option $\left(D\right)$ is correct.