Coral and algae need light in order for photosynthesis to take place. How to depth in the availability of light contribute to have these organisms are distributed on the ocean floor

Only blue light reaches deep into the ocean.

Explanation:

Coral reefs exist in waters less than 50 m to 2000 m deep while Red algae have been found living in depths of over 500 feet because both coral reefs and red algae needs blue light for photosynthesis. In the deep sea or ocean, only short wavelength such as blue light reaches deep in the ocean floor while long wavelength light such as red unable to reach so that's why both coral reefs and red algae present and distributed on the ocean floor.

the real answer is b. scintillation counter