The angle of refraction is 15.6 deg.
When a ray of light passes from medium 1 to medium 2, the refractive index of medium 2 with respect to 1 is the ratio of the absolute refractive index of medium 2 and medium 1

When light passes from air into diamond, with the given values of refractive indices,

According to Snell's law,

The angle of refraction is 15.6 deg