# In the Bohr model of H-atom, an electron (e) is revolving around a proton (p) with velocity v, if r is the radius of orbit and m is mass and $\varepsilon_0$ is vacuum permittivity, the value of v is :
$\begin{array}{1 1} (1)\; \frac{e}{\sqrt{4 \pi m \varepsilon_0 r}} \\ (2)\; \frac{2e}{\sqrt{\pi m \varepsilon_0 r}} \\ (3)\; \frac{e}{\sqrt{\pi m \varepsilon_0 r}} \\ (4)\; \frac{e}{4 \pi m \varepsilon_0 r} \end{array}$