In Hydrogen spectrum the shortest wavelength in Balmer series is λ . The shortest wavelength in the Brackett series will be
2λ
4λ
9λ
16λ
For shortest wavelength in Balmer series, n1=2, n2=∞
1λ=R142−1∞⇒λ=4R
For shortest wavelength in Brackett series, n1=4, n2=∞
∴1λ'=R142−1∞⇒λ'=16R=4λ