Which electronic level would allow the hydrogen atom to absorb a photon but not to emit a photon?

An isotone of $${}_{32}^{76}Ge$$ is

When alpha particles are sent through a thin metal foil, most of them go straight through the foil because

The electron energy in hydrogen atom is given by E = (-21.7 $$\times$$ 10^-12)/n² ergs. Calculate the energy required to remove an electron completely from the n = 2 orbit. What is the longest wavelength (in cm) of light that can be used to cause this transition?