1. The problem statement, all variables and given/known data Positronium is an atom formed by an electron and a positron. It is similar to the hydrogen atom, with the positron replacing the proton. If a positronium atom makes a transition from the state n = 3 to a state with n = 1, the energy of the photon emitted in this transition is closest to 3. The attempt at a solution what will my proton number Z be in this case? E = -13.6eV x Z2 / n2 but a hydrogen atom's Z = 1, what about the positronium atom? 0? state n=3 has -1.511 eV while state 1 has -13.6 eV. but the answer is 6 eV? how is that obtained? i have no idea . thanks for help!