On which of the following principles does optical fibre work?

Total Internal Reflection is correct. Optical fibers work on the principle of Total Internal Reflection (TIR). Light signals travel through the core (higher refractive index) and when they strike the core-cladding boundary at an angle greater than the critical angle, they are completely reflected back into the core. This allows light to travel long distances with minimal loss. Refraction would cause light to escape, scattering causes loss, and interference is not the principle.