If an electron is moving in the ${\mathrm{n}}^{\mathrm{th}}$ orbit of the Hydrogen atom, then its velocity $\left(v_n\right)$ for the ${\mathrm{n}}^{\mathrm{th}}$ orbit is given as:

In Bohr’s postulates  $\mathrm{mvr}=\frac{\mathrm{nh}}{2\mathrm{\pi }}$
And radius of Bohr orbit   $r \propto n^2$
Thus, velocity of electron  $v \propto \frac{1}{n}$, where n is orbit number