Question

The bluish color of water in deep sea is due to:
(A) The presence of algae and other plants found in water
(B) Reflection of sky in water
(C) Scattering of light
(D) Absorption of light by the sea

Answer 1

Hint
Water molecules absorb sunlight and scatter the different colours. Colours having longer wavelength can be absorbed easily whereas colors with lesser wavelengths will be scattered. The phenomenon for the colour of deep sea is similar to the phenomenon for colour of sky.

Complete step by step answer
Sunlight has seven visible colours i.e. red, orange, yellow, green, blue, indigo, and violet (Arranged according to decreasing wavelengths). Generally, water molecules absorb sunlight and scatter colours. The colours having longer wavelength are absorbed by water than those having shorter wavelengths. Red, orange, yellow, and green having longer wavelengths are absorbed by water molecules quickly when sunlight hits water. Since those colours are absorbed, the light we see consists of Blue, violet having shorter wavelengths. These colours are not absorbed but scattered by water. Thus, we can see water in blue colour in the deep sea.
Since blue colour of deep sea is mainly due to scattering, the correct answer is option (C) Scattering of light.

Additional Information
Rayleigh scattering relates to scattering by small particles, which says scattering $\propto {\displaystyle \frac{1}{{\lambda }^4}}$ , where $\lambda$ is wavelength of scattered particles.

Note
However, when water isn't pure, containing algae, plants and impurities this won’t be the case and the colour may be different as light scattered by those impurities also be taken into account.Even though the colour of sky and water are related, they occur independently. Sunlight contains very little amount of violet; this is the reason why even violet has lesser wavelength it gets dominated by blue.