The correct answer is option 'C' - Z. Let's understand why the magnetic field is in the Z direction in the Hall Effect.

1. The Hall Effect:
The Hall Effect is a phenomenon that occurs when a current-carrying conductor is placed in a magnetic field perpendicular to the current flow. It results in the generation of a voltage perpendicular to both the current and the magnetic field.

2. Electric Field and Current Direction:
In the given scenario, the electric field is in the x direction, and the velocity (which represents the current direction) is in the y direction. This means that the current is flowing in the y direction.

3. Force on Moving Charges:
When a current-carrying conductor is placed in a magnetic field, the moving charges experience a force due to the Lorentz force equation. This force acts perpendicular to both the velocity of the charges and the magnetic field.

4. Force Direction:
In this case, the force due to the magnetic field acts on the moving charges (current) in the y direction (perpendicular to the velocity in the y direction).

5. Magnetic Field Direction:
According to the right-hand rule, which determines the direction of the force on a moving charge in a magnetic field, the magnetic field must be in the Z direction (perpendicular to the x-y plane). This is because the force is in the y direction, and the electric field is in the x direction.

Conclusion:
In the Hall Effect, when the electric field is in the x direction and the velocity (current) is in the y direction, the magnetic field is in the Z direction (option 'C'). This is because the force on the moving charges due to the magnetic field is perpendicular to both the velocity and the magnetic field, as determined by the right-hand rule.