By using Snell's law, n1sinθ1=n2sinθ2, the refractive index is
μ=sin30∘sin45∘=2121=2
Also using the relation n=vc where n is the refractive index, c is the velocity of light in air and v is the velocity in the medium
⇒vcair =2=λ2λ1
The velocities are given by
v=νλ2c=νλ1
⇒λ1=2λ2 and ν1=ν2.
The frequency of light does not change when the medium changes.