When light is refracted into a denser medium,

The optical path of a particular ray of light that has travelled a distance of $3 \ cm$ in flint glass is the same as that of a ray travelling a distance of '$x$' $cm$ through another medium. The value of '$x$' is [refractive index of flint glass $= 1.6$, refractive index of another medium $= 1.25$]. (in $cm$)

The wavelength of light,while it is passing through water,is $540 \ nm$. The refractive index of water is $\frac{4}{3}$. The wavelength of the same light when it is passing through a transparent medium having a refractive index of $\frac{3}{2}$ is . . . . . . $nm$.

$A$ 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?

$A$ wave has velocity $u$ in medium $P$ and velocity $2u$ in medium $Q.$ If the wave is incident in medium $P$ at an angle of $30^\circ,$ then the angle of refraction will be .... $^o$

$A$ boat has a green light of wavelength $\lambda = 500 \ nm$ on the mast. What wavelength would be measured and what colour would be observed for this light as seen by a diver submerged in water by the side of the boat? Given,$n_{w} = 4/3$.