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# 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 :

( A ) $\large\frac{e}{\sqrt{4 \pi m \in_0 r}}$
( B ) $\large\frac{e}{\sqrt{\pi m \in_0 r}}$
( C ) $\large\frac{2e}{\sqrt{\pi m \in_0 r}}$
( D ) $\large\frac{e}{4 \pi m \in_0 r}$

$\large\frac{mv^2}{r}=\frac{1}{4 \pi \in_0} \frac{e^2}{r^2}$v^2= \large\frac{e}{\sqrt{4 \pi \in _0 r m }}\$