If the refractive indices for water and diamond relative to air are 1.33 and 2.4 respectively, then the refractive index of diamond relative to water is

The correct option is B 1.8
refractive index of water w.r.t. air is

${}_w{\mu }_a=\frac{{\mu }_w}{{\mu }_a}$ =1.33 (1)

similarly refractive index of diamond w.r.t. air is

${}_d{\mu }_a=\frac{{\mu }_d}{{\mu }_a}$ = 2.4 (2)

from (1) and (2)

divide equation (2) by equation (1)

we get,

${}_d{\mu }_w=\frac{{\mu }_d}{{\mu }_w}=\frac{{}_d{\mu }_a}{{}_w{\mu }_a}$

${}_d{\mu }_w=\frac{2.4}{1.33}=1.80$

refractive index of diamond with respect to water is 1.80

Option B is correct.