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The visible emission lines observed by Balmer all involved
nf = 2. (a) Which of the following is the best explanation of
why the lines with nf = 3 are not observed in the visible portion
of the spectrum: (i) Transitions to nf = 3 are not allowed
to happen, (ii) transitions to nf = 3 emit photons in the
infrared portion of the spectrum, (iii) transitions to nf = 3
emit photons in the ultraviolet portion of the spectrum, or
(iv) transitions to nf = 3 emit photons that are at exactly the
same wavelengths as those to nf = 2.