A layer of oil 3 cm thick is floating on a layer of colored water 5 cm thick. The refractive indices of colored is 5/3 and they apparently depth of two liquid is 36/7 .then the refractive index of oil is

refractive index =Real depth / Apparent depth

=Refractive index of coloured water(5/3) = Real depth(5cm) / Apparent depth

= Apparent depth of coloured water = 3cm

=Apparent depth of oil = Total apparent depth(36/7cm) - Apparent depth of coloured water(3cm)

=Apparent depth of oil=15/7cm

Refractive index of oil = Real depth of oil(3cm) /Apparent depth of oil(15/7cm)

=Refractive index of oil = 1.4