The lattice site in a pure crystal cannot be occupied by

Each point in a lattice, i.e. lattice point (which are either atom or molecule or ion) are. joined together by a straight line to bring out geometry of lattice. In pure crystal constituents are arranged in fixed stoichiometric ratio.
Hence, existence of free electrons are not possible, in case of pure crystals. It is possible only in case of imperfection in solid.