54) 91.2 nm
67) 4.66 x 1026 photons/s
68) 2.78 x 1021 photons/s•m2
80) 0.88 nm
83b) ground state; 0.4 eV, 2.2 eV, 2.5 eV; also 2.6 eV, 4.7 eV; and 5.1 eV
86) 3.33 x 1052 photons/year (wow!)