What happens when an oblique ray of light enters from glass into air?

$A$ point object emits rays in all directions. Consider a ray emitted from the object that is parallel to the principal axis of the mirror. One of the points required to trace the reflected ray is the point of incidence itself,as shown in the figure. Select a point from the given figure through which the reflected ray passes.

What is the effect on the wavelength of light when it travels from a rarer to a denser medium?

Under what condition in an arrangement of two plane mirrors,will the incident ray and the final reflected ray always be parallel to each other,regardless of the angle of incidence? Show the same with the help of a diagram.

What is the unit of refractive index?

Which type of mirror can produce a virtual image?