The wavelength of the fifth line in the Pfund series of a hydrogen atom is: (RH = 1.097 × 10⁷ m⁻¹)
Pfund series: n₁=5, fifth line n₂=10. ν̄ = 1.097×10⁷ (1/25 - 1/100) = 3.291×10⁵ m⁻¹. λ = 1/ν̄ = 3.039×10⁻⁶ m = 3039 nm.
Ref: NCERT Class 11 Chemistry > Chapter 2: Structure of Atom > Topic: Electronic Configuration - Aufbau Pauli Hund and Stability