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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 2nd Balmer line (n = 4 to n = 2) will be:

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

Correct answer: 488.9 nm

Solution

The wavelength of the second Balmer line can be calculated using the Rydberg formula for hydrogen, which shows that the wavelengths decrease as the initial energy level increases. Since the first Balmer line corresponds to a transition from n=3 to n=2, the second line from n=4 to n=2 will have a shorter wavelength, which is correctly calculated to be 488.9 nm.

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