$A$ wavefront is the locus of all points where the particles of the medium vibrate with the same:

Newton postulated his corpuscular theory on the basis of

Consider a point at the focal point of a convergent lens. Another convergent lens of short focal length is placed on the other side. What is the nature of the wavefronts emerging from the final image?

How can it be said that light possesses wave nature?

The main drawback of Huygens' theory was:

If $AB$ is an incident plane wave front,then what will be the refracted wave front for a lens with refractive index $n_2 > n_1$?