When light travels from one medium to another with a different refractive index, which of the following will change?

Explain rarer and denser medium.

$A$ beam of light is propagating at an angle $\alpha_1$ from medium $1$ into medium $2$ at an angle $\alpha_2$. If the wavelength of light in medium $1$ is $\lambda_1$, then the wavelength of light in medium $2$, $\lambda_2$, is:

$A$ beaker containing liquid is placed on a table,underneath a microscope which can be moved along a vertical scale. The microscope is focused,through the liquid,onto a mark on the table when the reading on the scale is $a$. It is next focused on the upper surface of the liquid and the reading is $b$. More liquid is added and the observations are repeated; the corresponding readings are $c$ and $d$. The refractive index of the liquid is

$A$ beam of monochromatic blue light of wavelength $4200 Å$ in air travels in water of refractive index $4/3$. Its wavelength in water will be: (in $Å$)

$A$ light wave travels through three transparent materials of equal thickness. Rank in order,from the highest to lowest,the indices of refraction $n_1, n_2$ and $n_3$.