When light passes from air into water, the frequency of the light remains the same. what happens to the speed and the wavelength of light as it crosses the boundary in going from air into water?

Let n₁ be the refractive index of air and n₂ be of water.
You already know that n₂>n₁ because light is bent towards normal in case of denser medium.

Speed of light in air(v₁) = c/n₁ c = ultimate speed limit of the universe which is speed of light in vacuum.

Speed of light in water(v₂) = c/n₂

Dividing both the relations,

v₁      c/n₁      n₂
--- =  = --- 
v₂      c/n₂      n₁

v₁/v₂ = n₂/n₁
∴ v₂ = v₁n₁/n₂ 

As n₂>n₁,
     v₂<v₁
So the speed of light slows down!

Ithink the answer would be a