Energy density is energy per unit volume.

Energy density=0 * E²/2

Forthe same electric field Beteween the plates of capicitor, Energy density is directly proportional to 0.

In the case of a dielectric,

Energy density =K0E²/2

Where K is the relative permitivity.

Thus energy Density in dielecric is K times that in vacuum.

energy capacitance which is  dielectric const.

for vaccum K(dielectric constant) is unity and capacitance of capacitor having dielectric between it is K times that in vaccum.

energy is K times that in vaccum.

as energy densityenery energy density is K times that in vaccum.