Q.

Which transition in the hydrogen spectrum would have the same wavelength as the Balmer-type transition from n=4 to n=2 of the He+ spectrum           [2023]

1 n=1 to n=3  
2 n=1 to n=2  
3 n=2 to n=1  
4 n=3 to n=4  

Ans.

(3)

λH=λHe+

RH×(1)2(1n12-1n22)=RH×(2)2(1(2)2-1(4)2)

(1n12-1n22)=(44)-(416)

1n12-1n22=11-14

n1=1,n2=2 for H-atom