Question

The ionic radius of $M{n}^{2+}$ ion is $0.082nm$ and that of $S^{2-}$ ion is $0.186nm$. The coordination number of the cation is:

• A. 6
• B. 8
• C. 4
• D. None of the above

Answer 1

The correct option is A 6

Radius ratio,
$\frac{r_{\left(M{n}^{2+}\right)}}{r_{\left(S^{2-}\right)}}=\frac{0.082}{0.186}=0.440$
For $NaCl$, $\frac{r_{+}}{r_{-}}=0.414to0.732$
Thus structure of the cubic unit cell is that of $NaCl$.
Note

Radius ratio	Coordination Number	Structure type
0.225 - 0.414 0.414 - 0.732 0.732 - 1.000	4 6 8	$ZnS$ $NaCl$ $CsCl$