Axelneo

Thanks for the help and for the welcoming, I did solve the problem and did it this way; I used Rydbergs formula, in which i put in energy as E=hc/lambda (multiplied both sides by hc) and after that it was pretty straight forward, just to plug in all of my values. Once again thanks.

I've gotten this problem of mine, which I cannot figure out myself, so I thought anyone here might be able to explain how it should be solved. The problem goes as follows: "When a hydrogen atom deexcitates to its ground state it emits an photon with the energy of 12.75 eV, what energy state did the atom have before the deexcitation?" I have tired and failed, the answer sould be that the atom was in its forth energy state, I would appreciate if someone explained how to approach such a problem and how to solve it, thanks.