Assertion: Propagation of light through an optical fiber is due to total internal reflection taking place at the core-clade interface.

Reason: Refractive index of the material of the core of the optical fiber is greater than that of cladding

In optical fibre communication, propagation of signalthrough optical fibre takesplace, which is based on thephenomenon of total internal reflection at core- cladeinterface.The refractive index of the material of the cladding is lessthan that of core, hence light striking at core-claddinginterface gets totally internally reflected.
Therefore, both A and R are true but R is not the correctexplanation of A.