Refractive index (n) is inversely proportional to velocity (v).
Let ni= Refractive index of liquid w.r.t air
ng= Refractive index of glass w.r.t air =1.5
vi= velocity of light in liquid =2.5×108 m s−1
vg= velocity of light in glass =2×108 m s−1
n α 1v
⟹nlng=vgvl
⟹nl1.5=2×1082.5×108=22.5=2025=45
⟹nl=1.5×0.8=1.5
∴ The refractive index of the liquid with respect to air is 1.5.