Maxwell’s modified form of Ampere’s circuital law is:

CONCEPT:

• Amperes law: The line integral of the magnetic field around any closed curve is equal to μ_o times the net current I threading through the area enclosed by the curve.

Ampere’s law in this form is not valid if the electric field at the surface varies with time.

• Displacement current (I_D): It is that current that comes into existence, in addition to the conduction current, whenever the electric field and hence the electric flux changes with time.

EXPLANATION:

• To modify Ampere’s law, Maxwell followed a symmetry consideration.
• By Faraday’s law, a changing magnetic field induces an electric field, hence a changing electric field must induce a magnetic field. As currents are the usual sources of the magnetic field, a changing electric field must be associated with the current. Maxwell called that current as displacement current.
• To maintain the dimensional consistency, the displacement current is added in ampere’s law: 

Where,  is the displacement current. So option 4 is correct.