Question

The wavelength of light that is least absorbed by the ocean is

• A. Red
• B. Blue
• C. Yellow
• D. Green

Hint:

Light Penetration in Ocean:
Least Absorbed (Deepest penetrating) = BLUE light ($400 - 480\text{ nm}$).
Most Rapidly Absorbed (Extinguished first) = RED light ($650 - 700\text{ nm}$).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Optical oceanography and underwater spectral attenuation: pure oceanic water has minimal optical absorption coefficients in the blue-violet spectral window ($400-480 ext{ nm}$), allowing blue light to penetrate deepest (up to 200 m).
Key Formula or Approach:
\[ I_z = I_0 e^{-k_\lambda \cdot z} \quad \implies \quad k_{\text{blue}} \approx 0.02\text{ m}^{-1} \text{ (Minimal Attenuation)} \ll k_{\text{red}} \approx 0.35\text{ m}^{-1} \]

Step 2: Detailed Explanation:
In optical oceanography and solar radiation penetration:
- Water molecules exhibit wavelength-dependent absorption of electromagnetic radiation:
1. Red Light ($650 - 700\text{ nm}$): Has the highest absorption coefficient; it is strongly and rapidly absorbed in the top $5 - 10\text{ meters}$ of the sea.
2. Blue Light ($400 - 480\text{ nm}$) (B): Has the lowest absorption coefficient (least absorbed by clear oceanic water).
- Because blue wavelengths are least absorbed and most widely scattered by water molecules, blue light penetrates deepest into the euphotic zone (up to $150 - 200\text{ m}$), giving open pelagic oceans their characteristic deep blue color.

Step 3: Final Answer:
Hence, the wavelength least absorbed by the ocean is Blue, matching option (B).