When the light ray passes from an optically lighter to denser medium, the light ra y bends towards the normal to the interface at the point of incidence. That means that the angle of refraction is less in the denser medium.
In the given example, medium 1 is the lighter one and medium2 is denser.
The actual reason for the bending of light ie., angle of refraction being smaller than angle of incidence is because of speed of light being less in a denser medium. Light rays travel with less speed due to optical resistance faced.
formula wise, μ₁ sin i = μ₂ sin r
i = x > r = x/2, so μ₂ > μ₁
so medium 1 is lighter as refractive index is less. Refractive index of vacuum (lightest) is 1 and all other media have that more than 1.