The correct option is A q(E0−B0vz)^i+qB0vx^k
In this region, the electric field will provide acceleration for the particle in +ve x−direction and once particle has some velocity in x−direction, the magnetic force will act on it in +ve z−direction (^k) as per q(→v×→B).
The particle will translate in x−direction, and it will rotate in xz plane.
At any time t, its velocity can be written as,
→v=vx^i+vz^k
Net force on the particle at this moment will be,
→F=→Fe+→Fm
⇒→F=q[E0^i+(vx^i+vz^k)×B0^j]
⇒→F=q[E0^i+(B0vx)^k−(B0vz)^i]
⇒→F=q(E0−B0vz)^i+qB0vx^k