An electron in a hydrogen atom is initially in the n=4 level and eventually returns to the ground state n=1 by making all possible downward transitions.
(a) How many distinct photon wavelengths can be emitted during this cascade?
(b) Identify which of these wavelengths corresponds to the lowest photon frequency and name the spectral series to which it belongs.
a. (a) Number of distinct wavelengths
b. (b) Wavelength of lowest frequency and its spectral series