On heating a liquid,the refractive index generally

An electromagnetic wave of wavelength $\lambda_0$ (in vacuum) passes from $P$ towards $Q$ crossing three different media of refractive index $\mu, 2\mu$ and $3\mu$ respectively as shown in the figure. Let $\phi_P$ and $\phi_Q$ be the phase of the wave at points $P$ and $Q$. Find the phase difference $\phi_Q - \phi_P$. [Take: $\mu = 1$]

If the wavelength of light in air is $4200\, \mathring A$,what will be the wavelength of light in water $(\mu = 4/3)$ in $\mathring A$?

Consider slabs of three media $A, B$ and $C$ arranged as shown in the figure. The refractive index $(R.I.)$ of $A$ is $1.5$ and that of $C$ is $1.4$. If the number of waves in $A$ is equal to the number of waves in the combination of $B$ and $C$,then the refractive index of $B$ is:

The ratio of the refractive index of red light to blue light in air is

When light travels from air to water,then from water to glass,then from glass to $CO_2$ gas,and finally back to air,the relation between their refractive indices is given by: