#### Answer

2.5 nm

#### Work Step by Step

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 = $10^{-9}$ ).