posted by natash .
How much energy is required to ionize a hydrogen atom in its ground (or lowest energy) state?
What wavelength of light contains enough energy in a single photon to ionize a hydrogen atom?
I would do the second part first.
1/lambda = R*(1/N^2 - 1/N^2).
You know the Rydberg constant, the first N is 1 and and N2 is infinity. Solve for lambda.
Then E = hc/lambda