What mechanism ensures that the light signal remains confined to the core of an optical fiber?

Correct option is C

​$$\text{In an optical fiber, light remains confined to the core due to Total Internal Reflection (TIR):} \\[8pt]\bullet \ \text{The core has a higher refractive index than the cladding.} \\[4pt]\bullet \ \text{When light traveling in the core strikes the core–cladding boundary at an angle greater than the critical angle, it undergoes total internal reflection.} \\[4pt]\bullet \ \text{Repeated TIR at this boundary guides the light signal along the length of the fiber with minimal loss.}$$​​