Why The outer rim of a Smith chart carries two scales, "wavelengths toward generator" and "wavelengths toward load," running from 0 to 0.5. They are graduated in fractions of an electrical wavelength on the transmission line, because impedance repeats every half wavelength as you move along the line. Moving a given fraction of a wavelength along the line corresponds to rotating that same fraction around the chart (a full trip around equals 0.5 wavelength).
Watch out The choices mentioning frequency are wrong because the chart is normalized and frequency independent; the antenna wavelength choice confuses the load with the line, and it is the line's electrical length, including its velocity factor, that the scale tracks.
Smith chart rim = wavelengths toward generator/load, 0 to 0.5, on the LINE. Line plus wavelength, not antenna, not frequency.