Which process is responsible for the ocean's blue color?

• A. Molecular Scattering
• B. Refraction
• C. Absorption by dissolved salts
• D. Reflection off the surface

Answer: (A)

Light from the Sun contains all colors, but when it hits the ocean the water molecules interact with the light and scatter some wavelengths in different directions. Shorter wavelengths, like blue, scatter more readily than longer wavelengths, so the scattered blue light is what you predominantly see when you look into the water. In deeper water, the longer red wavelengths are absorbed more strongly, leaving the blue-green light to dominate. So, the ocean’s blue appearance mainly comes from this scattering by water molecules. Refraction changes the light’s path but doesn’t select color, absorption by salts would affect color differently and isn’t the primary reason here, and surface reflection mostly mirrors the sky rather than giving the water its own color.