If $\hat{\mathrm{i}}$ denotes a unit vector along the incident light ray, $\hat{\mathrm{r}}$ a unit vector along refracted ray into a medium of refractive index $\mu$ and $\hat{\mathrm{n}}$ unit vector normal to the boundary of medium directed towards the incident medium, then the law of refraction is

Immiscible transparent liquids $A,B,C,D$ and $E$ are placed in a rectangular container of glass with the liquids making layers according to their densities. The refractive index of the liquids are shown in the adjoining diagram. The container is illuminated from the side and a small piece of glass having refractive index$1.61$ is gently dropped into the liquid layer. The glass piece as it descends downwards will not be visible in