Chapter 18 - The Micro/Macro Connection - Exercises and Problems - Page 523: 37

$61$

We know that $\frac{\lambda}{d}=\frac{k_BT}{8\pi \sqrt{2}p r^3}$ We plug in the known values to obtain: $\frac{\lambda}{d}=\frac{1.38\times 10^{-23}\times 298}{8\pi \sqrt{2} \times 1.52\times 10^7\times (5\times 10^{-11})^3}$ This simplifies to: $\frac{\lambda}{d}=61$