What happens when light is refracted into a medium?

The correct answer is Option (3) → The wavelength changes but the frequency remains unchanged

When light is refracted into a medium, the speed of the light and the wavelength changes due to different optical properties of the new medium.

$λ'=\frac{λ}{μ},v'=\frac{v}{μ}$ [$μ$ = Refractive index]

and,

$v=f.λ$ [f = frequency]

$⇒f=\frac{v}{λ}=\frac{v'}{f'}$