The simple unit of the electrical potential difference is Volt.
In terms of the charge and potential energy, the unit of electric potential is J/C.
In terms of the force and displacement, the unit of electric potential is Nm/C.
As the J/C is the unit of electric potential, thus, it is not possible to have units of C/J for the electric potential difference.
Thus, C/J is not valid unit for electrical potential difference.
Hence, option 4 (C/J) is the correct answer.