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Taking the wavelength of first Balmer line in hydrogen spectrum (n = 3 to n = 2) as 660 nm, the wavelength of the 2 nd Balmer line (n = 4 to n = 2) will be :

1. 889.2 nm
2. 388.9 nm
3. 488.9 nm
4. 642.7 nm

Correct answer: 488.9 nm

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