The working of an optical fibre can be explained on the basis of

The correct answer is Option (4) → Total Internal Reflection of Light

An optical fibre has a glass core surrounded by a cladding of lower refractive index. Light entering the core strikes the core-cladding boundary at an angle larger than the critical angle, so it suffers total internal reflection. It is reflected again and again along the fibre with almost no loss, even when the fibre is bent.

NCERT (2026-27):
Total Internal Reflection in Nature and Its Technological Applications – “… Nowadays optical fibres are extensively used for transmitting audio and video signals through long distances. Optical fibres too make use of the phenomenon of total internal reflection. … Since light undergoes total internal reflection at each stage, there is no appreciable loss in the intensity of the light signal.”