Answer
See explanation.
Work Step by Step
As explained in the section on Gauss’s Law, the electric field inside a conductor is always zero in an electrostatic situation. This answer holds no matter how much excess charge it carries.
Since the electric field is zero, it takes no work to move test charges within the conductor, and the electric potential does not vary from point to point within the material.
The cavity inside the conductor contains no charge, so the electric field within it is also zero, and the electric potential is also the same everywhere within it.
With zero electric field everywhere inside the object, the electric potential inside the cavity and inside the material must have the same value.
