Your question has two parts and I would answer both in short.The dielectric slab is obviously an insulator, the unequal charges I.e.,lesser than what were on the capacitor plates would be induced on the surface of slab along with few electric field lines of force passing through the volume of the slab.Any text book explains all this.Young student try to think out of the box.Put some good questions the answers to which are not enlisted on text books.