Question

If refractive index of water is value of ref. index (0.75) of air w.r.t. glass.

Answer 1

water with ref. to air=0.75=3/4
air with refer. to water=4/3 
since refractive index of water with ref. to air * refractive index of air to water =1
therefore the answer=4/3 or 1.333