An electron remains undeflected when passing perpendicular to mutually perpendicular electric and magnetic fields. If the magnetic field is 8 Gauss and the electric field is $400\; V/m$, the velocity of the electron is :

Question

( A ) $6 \times 10^6\; m/s$
( B ) $2 \times 10^6\; m/s$
( C ) $7.5 \times 10^6\; m/s$
( D ) $5 \times 10^5\; m/s$