Depending upon the mode of nutrition, Algae falls under
a. Photoautotrophs
b. Chemoautotrophs
c. Detritivores
d. Parasites

Hint: Algae prepare their food with the help of sunlight and carbon dioxide. They do not require dead organic materials for generating their energy. Algae also cannot oxidize the inorganic molecules such as iron, sulfur, etc. And the main thing is they do not depend upon other organisms for food.

Complete answer:
- As algae belong to the photoautotrophs. Algae prepare their food with the help of photosynthesis. Their main requirement is sunlight which helps the algae to make their food.

- Photoautotrophs are the kind of organism which can make their food, but their basic requirements are sunlight and carbon dioxide.

- The second option is chemoautotrophs, as this is the wrong answer because algae do not synthesize their food with the help of the fixation of carbon dioxide.

- Algae cannot do the oxidation of various inorganic molecules such as iron and sulfur or magnesium. Hence this option is wrong.

- The next option is detritivores which are also not the right answer because algae do not feed on the dead organic matter as they produce their food, that’s why this option is also wrong.

Hence, The correct answer is option (A).

Note:
- The photoautotrophs word is made by the combination of the two words, first is a photo that means the light and the other is autotrophs whose meaning is the organism who can make their food.
- Algae are the most diverse form of life which is found in the aquatic regions and can do photosynthesis. The most common algae are the seaweeds.