Question

Radius ratio of $\left(\frac{A^{+}}{B^{-}}\right)=\frac{0.98\times {10}^{-10} m}{1.81\times {10}^{-10} m}=\frac{0.98}{1.81}=0.541$
If the radius ratio is between 0.414 and 0.732 then Co-ordination number is 6.