Consider a hydrogen-like ionized atom with atomic number Z with a single electron. In the emission  spectrum of this atom, the photon emitted in the  n=2  to  n=1 transition has energy  74.8eV  higher  than  the  photon  emitted  in  the  n=3  to  n=2 transition.  The ionization energy of the hydrogen atom is  13.6eV. The value of Z is .