Answer
$3.84\times10^{14}s^{-1}$
Work Step by Step
ν = $\frac{c}{λ}$
c = $2.997925\times10^{8}ms^{-1}$
λ = $7.80\times10^{2}nm$ = $7.80\times10^{2}\times10^{-9}m$ = $7.80\times10^{-7}m$
ν = $\frac{2.997925\times10^{8}ms^{-1}}{7.80\times10^{-7}m}$ = $3.84\times10^{14}s^{-1}$
