Electric Dipole

The drift velocity of electrons denotes the average speed at which free electrons move in a conductor when subjected to an electric field. When a voltage is applied to a conductor, the resulting electric field accelerates free electrons, causing them to move in the direction of the electric field.
Yet, collisions with atoms and other electrons within the conductor prevent free electrons from maintaining a constant velocity. Instead, they exhibit a small, average velocity in the direction of the electric field, termed the drift velocity.
The movement of free electrons in a conductor is impeded by collisions with atoms and other electrons, preventing them from maintaining a constant velocity. Instead, they exhibit a small, average velocity in the direction of the electric field, known as the drift velocity.
Therefore, the drift velocity of electrons is directly proportional to the voltage applied across a conductor.
So, the correct option is (B) : Voltage applied.