Whar are two longest wavelength in frequency 1kghz and 200kghz
You should clarify the question. As stated I can't make sense of it. Do you want to convert frequency to wavelength? If so then C = freq x wavelength
c = 3E8 m/s
freq = 1E12 or 200E12
Solve for wavelength
By the way a kghz (or kGHz or kilogigaherz) is a THz or teraherz.