If the question was that why are some materials opaque and why some are transparent, the answer would be found in the energy bands. If energy bands allow such transitions for electrons, that they can absorb photon, then they will absorb it, and the photon does not go through the material. If electrons instead cannot absorb a photon, then the photon will go through the material. Was that right? Well then the next question is that why are some materials reflective and some absorptive? Can it be explained with the energy bands?