The incorrect statement about the refractive index for a pair of media is:

If $_i{\mu _j}$ represents the refractive index when a light ray goes from medium $i$ to medium $j,$ then the product $_2{\mu _1} \times {\,_3}{\mu _2} \times {\,_4}{\mu _3}$ is equal to

Monochromatic light is refracted from air into glass of refractive index $\mu$. The ratio of the wavelength of incident and refracted waves is

$A$ ray of light passes from the vacuum into a medium of refractive index $n$. If the angle of incidence is twice the angle of refraction, then the angle of incidence in terms of refractive index is

$A$ ray of light travels from air to water to glass and again from glass to air. The refractive index of water with respect to air is $x$,glass with respect to water is $y$,and air with respect to glass is $z$. Which one of the following is correct?

$A$ monochromatic light of frequency $5 \times 10^{14} \ Hz$ travelling through air is incident on a medium of refractive index $2$. What will be the wavelength of the refracted light (in $nm$)?