Q.As per recent understanding light consists of (A) rays (B) waves (C) corpuscles (D) photons obeying the rules of waves

Light was historically defined only by its effect -- 'that form of radiant energy which makes objects visible by stimulating the retina' -- rather than by what it actually IS. Two independent lines of 20th-century physics settled the question, and together they give the modern, dual picture. First, light was shown to be an electromagnetic (EM) wave, propagating even through vacuum at the universal speed $c=299792458\ \text{m/s}\approx3\times10^8\ \text{m/s}$ (the maximum possible speed for anything, per Einstein's special relativity). Second, using experiments with countable numbers of photons, quantum theory established that light also carries energy in discrete packets, called photons.

Neither picture alone is sufficient: light is not simply a stream of tiny 'corpuscles' in the old Newtonian sense (this fails to explain interference and diffraction), nor is it simply a classical wave (this fails to explain the photoelectric effect and other quantum phenomena). The correct modern synthesis is that light consists of photons -- particles carrying discrete energy -- whose propagation and interaction obey the mathematical rules of electromagnetic wave theory.

Inside any material medium, the wave's speed is set by the medium's permittivity and permeability, always slower than in vacuum; this slowing defines the medium's absolute refractive index, $n=c/v$. Depending on which behaviour is being studied, light phenomena are grouped into three headings: RAY (geometrical) optics for reflection/refraction/TIR (this chapter); WAVE (physical) optics for interference/diffraction/polarization (Class XII); and the PARTICLE nature of light for the photoelectric effect, spectral emission and the Compton effect (also Class XII).