What physical quantity is the same for X-rays of wavelength `10^(–10)m`, red light of wavelength `6800 Å` and radiowaves of wavelength 500m?

Explanation

All of given radiations have equal speed in vacuum, given by `c=3xx10^(8)m//s`.
Note : Here in the statement, actually they should have given that all the radiations propagate in the same medium or propagate in vacuum. (If these radiations propagate in different media then their speeds would be different). While propagating in the same medium if thier equal speed is v then `v lt c`.