why light does not bent when it strike any object perpendicularly

Snell`s law states that the ratio of the sines of the angles of incidence and refraction is equivalent to the ratio of phase velocities in the two media, or equivalent to the reciprocal of the ratio of the indices of refraction.Hence according to Snell`s law there is no change in the phase when light strikes any object perpendicularly.

According to the law of reflection angle of incidence is always equal to the angle of reflectionTherefore when the light strikes perpendicular to the mirrorThe angle of incidence is 90° and hence angle of reflection is 90°Then light retraces it`s path