Atomic Spectra

Step 1: Understanding the Rydberg series.
Rydberg atoms are highly excited hydrogen-like atoms with large values of . When the atom transitions between adjacent energy levels, the emitted radiation moves to the radio frequency (RF) range for such large values of , with wavelengths on the order of meters ( ).
Step 2: Conclusion.
Therefore, the correct answer is option (D), as the radiation lies in the RF range for these transitions.