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In the hydrogen spectrum, the longest wavelength in the ultraviolet region is 122 nm. The shortest wavelength in the infrared region, rounded to the nearest whole number, is

1. 802 nm
2. 823 nm
3. 1882 nm
4. 1648 nm

Correct answer: 823 nm

Solution

Longest UV is Lyman 2->1: 1/122 = R(3/4) -> R = 1/91.5 nm^-1. Shortest IR is the Paschen series limit (inf->3): lambda = 9/R = 9*91.5 = 823 nm.

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