Huygens' principle of secondary wavelets may be used to

Explain the refraction of a plane wave by a thin prism.

The idea of secondary wavelets for the propagation of a wave was first given by

$A$ point source of light is placed at the focus of a concave mirror. Consider only paraxial rays. The shapes of the wavefronts of incident and reflected lights respectively are

$A$ parallel cylindrical beam of light propagates in a medium with a refractive index $\mu(I) = \mu_0 + \mu_2 I$,where $\mu_0$ and $\mu_2$ are positive constants and $I$ is the intensity. As the intensity of the light decreases,the radius increases. The initial shape of the wavefront is:

How can it be said that light possesses wave nature?