On heating a liquid,the refractive index generally

The phase difference between the incident wave and the reflected wave is $180^o$ when a light ray:

$A$ 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?

The index of refraction of diamond is $2.0$. The velocity of light in diamond in $cm/s$ is approximately:

$A$ 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 $nm$)?

Refractive index of a medium is $\mu$. If the angle of incidence is twice that of the angle of refraction, then the angle of incidence is