Answer: The correct answer is "a moving charged particle".
Explanation:
If the current flowing in the conductor then there is magnetic field around the wire which can be detected by the compass needle.
Here, the flow of charges which are negatively charged electrons produces the magnetic field. The flow of charges constitutes the electric current.
If there is no flow of the charged particles then there is no magnetic field produce. To produce magnetic field, it is necessary that charged particle must move.
From the given options, a moving charged particle would produce a magnetic field.
Therefore, the correct option is (4).
