Chapter 7 - Electronic Structure - Questions and Exercises - Exercises - Page 286: 7.42

2.5 nm

λ = $\frac{h}{mv}$ h = $6.626\times10^{-34}Js$ v = $2.9\times10^{5}m/s$ m = $9.109\times10^{-31}kg$ λ = $\frac{6.626\times10^{-34}Js}{9.109\times10^{-31}kg\times2.9\times10^{5}m/s}$ = $2.5\times10^{-9}m$ = 2.5 nanometers ( nano = $10^{-9}$ ).