An electron moving in a circular orbit of radius r makes n rotations per second. The magnetic field produced at the centre has magnitude

Magnetic field at center of circular coil is given as→B=μ∘I2rwhere I is current in coil.time taken in n revolution is 1 sec, time taken in 1 rev=1nI=qt=e1n→B=μ∘ne2rhence, correct answer is option B.