Explanation: The speed of electromagnetic waves is given by

where ν is the frequency and λ is the wavelength. Thus the speed

will be not same for all frequencies and wavelengths so A. and D.

are incorrect. Also as wave travels from one medium to another, the

speed changes so B. is incorrect. The relation between speed and

intensity of a wave is given by

where ϵ₀ is the electric permittivity of free space(vacuum) and is equal to 8.85 × 10^-12 C² N^-1 m^-2, c is the speed of wave and E₀ is the amplitude of electric field. The speed will be same for all intensities in a given medium will be same so C. is correct.