When light enters glass from vacuum,then the wavelength of light

The velocity of light in glass having a refractive index of $1.5$ is $2 \times 10^8 \ m/s$. What is the refractive index of a liquid in which the velocity of light is $2.50 \times 10^8 \ m/s$?

An infinitely long cylinder of radius $R$ is made of an unusual exotic material with refractive index $-1$ (See figure). The cylinder is placed between two planes whose normals are along the $y$-direction. The center of the cylinder $O$ lies along the $y$-axis. $A$ narrow laser beam is directed along the $y$-direction from the lower plate. The laser source is at a horizontal distance $x$ from the diameter in the $y$-direction. Find the range of $x$ such that light emitted from the lower plane does not reach the upper plane.

The refractive index of water is $1.33$. The direction in which a man under water should look to see the setting sun is

$A$ large square container with thin transparent vertical walls and filled with water (refractive index $\mu = \frac{4}{3}$) is kept on a horizontal table. $A$ student holds a thin straight wire vertically inside the water at a distance of $12 \ cm$ from one of its corners,as shown in the figure. Looking at the wire from this corner,another student sees two images of the wire,located symmetrically on each side of the line of sight. The separation (in $cm$) between these images is:

What is refraction of light? Explain the laws of refraction.