When a ray of light passes from air to denser medium, its speed is reduced by 30%. What is the refractive index of the medium?

When a ray of light from air enters a denser medium, it :

When a ray of light passes from air medium to denser medium then its speed and wavelength

When light passes from a denser medium to a rarer medium

When a ray of light passes from air medium to denser medium then the refractive index is

The speed of light in a transparent medium is 0.6 times that of its speed in vacuum. What is the refractive index of the medium?

A ray of light, after passing through a medium, meets the surface separating the medium from air at an angle of 45^(@) and is just not refracted. What is the refractive index of the medium?