13. Red light is emitted from a gas discharge tube filled with hydrogen when electrons in the hydrogen jump down from the n=3 shell to the n=2 shell. The red light has a wavelength of 656 nm, the energy of the n=3 shell is -1.51 ev, and the energy of the n=2 shell is -3.40 eV. What is the energy of the emitted photon? A) 1.51 eV B) 1.89 ev C) 3.40 ev D) 4.91 ev E) 6.56 ev