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Hydrogen ( 1 H 1 ). Deuterium ( 1 H 2 ), singly ionised Helium ( 2 He 4 ) + and doubly ionised lithium ( 3 Li 6 ) ++ all have one electron around the nucleus. Consider and electron transition from n = 2 to n = 1. If the wavelengths of emitted radiation are λ 1 , λ 2 , λ 3 and λ 4 respectively then approximately which one of the following is correct ?

1. λ 1 = 2 λ 2 = 2 λ 3 = λ 4
2. λ 1 = λ 2 = 4 λ 3 = 9 λ 4
3. λ 1 = 2 λ 2 = 3 λ 3 = 4 λ 4
4. 4 λ 1 = 2 λ 2 = 2 λ 3 = λ 4

Correct answer: λ 1 = λ 2 = 4 λ 3 = 9 λ 4

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