The frequency of revolution of the electron in Bohr's orbit varies with n, the principal quantum number as 

The frequency of revolution of an electron in Bohr's orbit can be derived using the Bohr model of the hydrogen atom.

The frequency of revolution ($\nu$) is given by:

$$\nu = \frac{\text{velocity of electron} (v)}{\text{circumference of orbit} (2\pi r)}$$

Velocity of the electron in the $n$th orbit:

1. $$v_n = \frac{e^2}{2\epsilon_0 h} \times \frac{1}{n}$$

Since $v_n \propto \frac{1}{n}$.

Radius of the $n$th orbit:

1. $$r_n = \frac{n^2 h^2 \epsilon_0}{\pi m e^2}$$

Since $r_n \propto n^2$.

 Substituting in the Frequency Formula

$$\nu_n = \frac{v_n}{2\pi r_n}$$

Since $v_n \propto \frac{1}{n}$ and $r_n \propto n^2$, we get:

$$\nu_n \propto \frac{1/n}{n^2} = \frac{1}{n^3}$$