A parallel-plate capacitor is first charged by a battery and then disconnected from it. A dielectric slab with dielectric constant κ>1 is inserted so that it completely fills the space between the plates. Which of the following best describes what happens to the quantities listed?
a) Q remains the same, ΔV increases, and the stored energy increases.
b) Q remains the same, ΔV decreases, and the stored energy decreases.
c) Q increases, ΔV stays the same, and the stored energy increases.
d) Q remains the same, ΔV decreases, and the stored energy increases.