n=2 to n=1For the transition in the hydrogen-like atom, the wavelength of the emitted radiation is calculated byλ1​=RZ2(n1​1​−n2​1​) Here, R is the Rydberg constant.For the transition from n=5 to n=4, the wavelength is given by​λ1​=RZ2(421​−521​)λ=9RZ2400​​ For the transition from n=4 to n=3, the wavelength is given by λ1​=RZ2(321​−421​) λ=7RZ2144​ For the transition from n=3 to n=2, the wavelength is given by frac1λ=RZ2(221​−321​) λ=5RZ236​ For the transition from n=2 to n=1, the wavelength is given by λ1​=RZ2(121​−221​) λ=RZ22​ From the above calculations, it can be observed that the wavelength of the radiation emitted for the transition from n=2 to n=1 will be minimum.