Which of the following will not travel with the  speed of light? 

Concept:

• Speed of light: It is the speed at which light waves propagate through different materials.
  • The speed of light (when it is traveling in a vacuum) is 299792 kilometers per second.
  • It is often approximated to 3×10⁸ meters per second. 
• Electromagnetic spectrum: It is the arrangement of electromagnetic radiations according to their frequency or wavelength.
  • ​The electromagnetic spectrum has a range of frequencies, wavelengths, and photon energies.
  • Typically, electromagnetic waves travel at the speed of light in a vacuum. 
  • The electromagnetic spectrum is as follows: 

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• De Broglie's hypothesis: It postulates that any particle of matter that has linear momentum is also a wave.
  • The wavelength of a matter-wave associated with a particle is inversely proportional to the magnitude of the particle's linear momentum.
  • The speed of the matter-wave is the speed of the particle.

λ = h/p

Where p is the linear momentum, h = planks constant.

Explanation:

From the above discussion

• All electromagnetic waves rays like x-ray, gamma-ray, visible spectrum all travel with the light speed.
• De Broglie's hypothesis says that these waves do not travel at light speed.

So, the correct option is de Broglie's wave.