Which has more energy: a granite or concrete slab of the same volume, raised to the same height? How many times?

Both plates have potential energy. The potential energy depends on two factors: the height to which this body was lifted, and the mass of the body itself. Since, according to the condition of the problem, both plates are raised to the same height, in this case, only the mass plays a role.

Since both slabs are of the same volume, their mass will depend on the density of the material from which these slabs are made. The density of granite is 2600 kg / m3, the density of concrete (depending on the brand) is 2300 kg / m3 (average value for heavy concrete). This means that a granite slab will have 2600/2300 = 1.1 times the potential energy.