You slide a slab of dielectric between the plates of a parallel-plate capacitor. As you do this, the potential difference between the plates remains constant. What effect does adding the dielectric have on the amount of charge on each of the capacitor plates

In this scenario adding the dielectric material in between the plates will have no effect on the capacitance of the plates since the voltage remains unchanged

Explanation:

Normally Introducing a dielectric into a capacitor decreases the electric field, which decreases the voltage, which increases the capacitance.

A capacitor with a dielectric stores the same charge as one without a dielectric, but at a lower voltage.

Voltage and capacitance are inversely proportional when charge is constant.

Now in this case the voltage remains the same hence the charges remain the same also because voltage is inversely proportional to capacitance