what is the wavelength of a photon emitted during a transition from the initial state(ni)=5 state to the final state(nf)=2 state in the hydrogen atom?

Answer 1

1/wavelength = R[1(2)^2 - (1/5)^2]
R is the Rydberg constant. You can find that on Google. It's about 1.097E7
Post your work if you get stuck.