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Wavelength of light needed to ionize hydrogen from ground state (13.6 eV):

A400 nm
B91.2 nm (UV)
C656 nm
D121 nm
Answer & Solution
Correct answer: B. 91.2 nm (UV)
Energy = 13.6 eV. λ = hc/E. Use hc = 1240 eV nm: λ = 1240/13.6 ≈ 91.2 nm (ultraviolet). Sometimes called Lyman alpha continuum threshold.
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