When light waves suffer reflection at the interface between air and glass, the change of phase of the reflected wave is equal to
a)	Zero	b)		c)		d)

(c)

When light waves are incident on the interface between air and glass, then for the first ray there is no phase change on reflection from such an interface. The second ray is reflected at an interface between an optically less dense medium (air) through which the ray travels and a dense medium (glass). There is a  phase change on reflection from such an interface.