Solution

Phytoplankton are the producers in the ocean. Diatoms are a class of phytoplankton which are known as chief producers in the ocean. The food chain in a marine ecosystem depends on it. Thus, diatoms have left behind a large amount of cell wall deposits in their habitat; this accumulation over billions of years is referred to as ‘diatomaceous earth’. Being gritty this soil is used in polishing, filtration of oils and syrups. Thus, the correct answer is option 4.