The bluish colour 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
The colours with smaller wavelengths are scattered easily through the water bodies, making them appear blue.
The phenomenon is called Rayleigh Scattering.
So, the correct answer is (c)