Here, energy of electrons is inversely proportional to wavelength i.e. greater the difference between the transition, lesser will be the wavelength. Δn⇒n4−n3=n1 n4→n2=n2 n4→n1=n3 i.e. highest energy level transition n2→n1=n1 ∴ n4→n1 having higher energy level transition. So, it has least wavelength