A material particle with a rest mass m0 is moving with a velocity of light c. Then, the wavelength of the de Broglie wave associated with it is

We know that mass m in motion and the rest mass m0 is related through the equationm=m01−v2c2 As  v=c,m=m01−1=m00=∞Therefore, de Broglie wavelength isλ=hmv=h(∞)(c)=0