Question

The radius of \( \mathrm{Na}^{+} \) is 95 pm and that of \( \mathrm{Cl}^{-} \) ion is 181 pm. The coordination number of Na is:

• A. 8
• B. 6
• C. 4
• D. unpredictable

Hint:

Radius ratio 0.414 – 0.732 = Octahedral Geometry (C.N. 6).

Answer 1

The Correct Option is B

Step 1: Concept
The coordination number is determined by the radius ratio ($\frac{r_{+}}{r_{-}}$).
Step 2: Analysis
The radius ratio $\frac{r_{Na^{+}}}{r_{Cl^{-}}} = \frac{95}{181} = 0.524$. This value lies between 0.414 and 0.732.
Step 3: Conclusion
For a radius ratio in this range, the coordination number is 6.
Final Answer: (B)