It is well known that lightning is seen before the thunder is heard. Wavelengths of electromagnetic and sound waves can be the same. Imagine that the wavelengths from the lightning and thunder are the same, what can be said about their frequencies?

the frequency of thunder is more than the frequency of lightning

Explanation:

Light waves (lightning) are faster than sound waves (thunder). If their wavelengths are the same, then the frequency of light waves must be larger

Lightning is seen before the thunder is heard because, velocity of light exceeds velocity of sound. We also know that velocity, wavelength and frequency are related as follows

velocity = frequency x wavelength

velocity of light > velocity of sound

frequency of light x wavelength of light > frequency of sound x wavelength of sound

But given wavelength of light = wavelength of sound

Putting this relation in the equation above

frequency of light x wavelength of light > frequency of sound x wavelength of light

cancelling out equal terms on both sides

frequency of light > frequency of sound

frequency of light will be greater than frequency of sound.