The de Broglie wavelength of an electron moving in a circular orbit is $\lambda$. The minimum radius of orbit is:

De Broglie wavelength of an electron, ⁣$/$lambda

The minimum radius of orbit is found as,

$2\pi r=n\lambda ;r_{min}$

$n=1$

$r=\frac{\lambda }{2\pi }$

Hence, option B is correct.