velocity of electron moving around a proton in hydrogen atom in an orbit of radius $5.3 \times 10^{-11} \,m$ is $2.2 \times 10^{-6}\, m / s$. Thus, the frequency of the electron moving around the proton is

$v=\frac{v}{2 \pi r} =\frac{2.2 \times 10^{6} \,m s ^{-1}}{2 \pi\left(5.3 \times 10^{-11} \,m \right)}$

$ \approx 6.6 \times 10^{15} \,Hz$

According to the classical electromagnetic theory we know that the frequency of the electromagnetic waves emitted by the revolving electrons is equal to the frequency of its revolution around the nucleus. Thus the initial frequency of the light emitted is $6.6 \times 10^{15}\, Hz$