What transition in the hydrogen spectrum would have the same wavelength as the Balmer transition `n=4` to `n=2` of `He^(+)` spectrum ?

Explanation

For `He^(+)`,`Z=2 `" "`(1)/lambda=R_(H)Z^(2)[(1)/2^(2)-(1)/4^(2)]` ltBrgt For H,`Z=1` `(1)/lambda=R_(H)[(1)/n_(1)^(2)-(1)/n_(2)^(2)]`
since `lambda` is same
`therefore` `4[(1)/2^(2)-(1)/4^(2)]=[(1)/n_(1)^(2)-(1)/n_(2)^(2)]` ltBrgt `therefore` `[(1)/1^(2)-(1)/2^(2)]=[(1)/n_(1)^(2)-(1)/n_(2)^(2)]`` therefore` `n_(1)=1`and `n_(2)=2`