Why is oil immersed objective preferred in a microscope?

Explanation

(i) The ability of microscope depends not only in magnifying the object but also in resolving two points on the object separated by a small distance `d_("min")`(ii) Smaller the value of `d_("min")` better will be the resolving power of the microscope. (iii) To reduce the value of `d_("min") ` the optical path of the light is increased by immersing the objective of the microscope into a bath containing oil of refractive index n. (iv) Resolution of microscope could be improved by using oil immersed eye piece.