The number of spectral lines in the Brackett series when an electron falls from n = 7 to n = 4 in a hydrogen atom is:
Transitions: 7→4, 7→5→4, 7→6→4, 6→4, 5→4. Total = 5.
Ref: NCERT Class 11 Chemistry > Chapter 2: Structure of Atom > Topic: Shapes of Orbitals - s p d f and Nodes and Radial Probability