The ratio of the wave numbers of the radiation corresponding to the third line of Balmer series and the second line of the Paschen series of hydrogen spectrum is:
A
21/16 x 9/4
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B
25/16 x 9/4
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C
21/25 x 9/4
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D
16/25 x 9/4
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Solution
The correct option is A 21/16 x 9/4 Use the formula, Wavenumber = R×(1/n21−1/n22). For third line Balmer series n1=2 and n2=5. For second line Paschen series n1=3 and n2=5 Therefore the ratio is (1/4−1/25)/(1/9−1/25) which equals 21/16×9/4.