Refraction: The bending of light or change in the direction of propagation of light as it moves from one medium to another is called refraction.
Snell's law or the law of refraction states that the ratio of the sine of the angle of incidence (i) to the sine of the angle of refraction (r) is constant for a light of given wavelength travelling in a given pair of media.
= constant = µ
Where μ = refractive index of the second medium with respect to the first medium.
EXPLANATION:
From the above, it is clear that the sine of the angle of incidence divided by the sine of the angle of refraction equals refractive index is called Snell's law. Therefore option 1 is correct.