A charged particle goes undeflected in a region containing electric and magnetic field. It is possible that

Let us consider the electric field is parallel to the magnetic field. In this case the charges particle will accelerate and also it will move in same direction. Then it cannot deflect. If electric field is not parallel to magnetic field means that may be in perpendicular to each other. In this case magnetic field, electric field and velocity of a particle will be in perpendicular to each other. If both forces are equal, then force acting on the particle will be zero. Then particle will not deflect. So option A and B are correct. Option C and D are not valid conditions.

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