Given,
Wavelength of monochromatic light,
(a) For reflected light,
Wavelength is going to remain the same for incident and reflected light.
Wavelength,
Speed of lightwill remain invariant in two media.
Therefore,
(b) For refracted light,
Refractive index of water w.r.t. air,
i.e.,
So, wavelength of light
As frequency remains unaffected on entering another medium, therefore,
Speed,
i.e., speed of the light has decresed when it entered the second medium.