AIIMS 2019 Physics Capacitors and Dielectrics Assertion Reason Question

The assertion is true because when a dielectric slab with dielectric constant $k$ is introduced into a parallel plate capacitor connected to a battery, the energy stored in the capacitor increases by a factor of $k$ due to the reduction in electric field and increase in capacitance. However, the reason is false; the surface charge density on the plates does not remain constant when a dielectric is introduced, as the battery maintains a constant voltage, leading to a change in charge density. Therefore, while both statements are true, the reason does not correctly explain the assertion, making option C the correct choice. Options A and B are incorrect because they imply a correct relationship between the assertion and reason, while option D is incorrect since the assertion is indeed true.