Question

if we pass ray of light from oil drop then what will happen???

Answer 1

the light ray will refract because the light ray is travelling from rarer  media to denser media.

Answer 2

When a light ray passes through an oil drop, it acts like a prism (spherical).  The light rays from air are refracted. They are also reflected.  Then some refracted rays go through the other end of oil drop.
Some rays incident at suitable angles can produce dispersion of light. The light rays may get totally internally reflected.        
It depends on the angle of incidence and thickness of oil drop