Question

Define wabefront. use huygens's principle to verify the law of reflection.

Answer 1

a surface containing points affected in the same way by a wave at a given time.
laws of reflection on the basis of wave theory:

The angle of reflection r is equal to the angle of incidence i for all wavelengths and for any pairs of materials. 
r=i
hygiene made some assumptions that are
Each point on a wave front acts as a new source of the disturbance. The disturbances from these points are secondary wave lets. These wavelets spread out in all directions in the medium with the velocity of light.The new wave front is then obtained by constructing a tangential plane to all the secondary wavelets. The new wave front is the envelope of to secondary wavelets at that instant.

The incident ray, reflected ray and normal to the reflecting surface all lie on the same plane.