Which of the following electromagnetic waves has the highest...

The electromagnetic spectrum ordered by increasing frequency (or decreasing wavelength) is: Radio waves $<$ Microwaves $<$ Infrared rays $<$ Visible light $<$ Ultraviolet rays $<$ X-rays $<$ Gamma rays.

Among the given options, X-rays are located nearest to the high-frequency end of the spectrum, meaning they have the highest frequency.

Answer: X-rays