Chemistry: Principles and Practice (3rd Edition)

$3\times10^{7}s^{-1}$
λ = 10m c = $2.997925\times10^{8}ms^{-1}$ ν = c/λ = $\frac{2.997925\times10^{8}ms^{-1}}{10m}$ = $3\times10^{7}s^{-1}$