An alga which can be employed as food for human beings is Ulothrix, Goniodoma, Chlorella, Polysiphonia?

The correct option is C. Chlorella.

Chlorella is a genus of single-cell green algae belonging to the phylum Chlorophyta. It is spherical in shape, about 2 to 10 µm in diameter, and is without flagella. Chlorella contains the green photosynthetic pigments chlorophyll a and b in its chloroplast. Through photosynthesis, it multiplies rapidly, requiring only carbon dioxide, water, sunlight, and a small amount of minerals to reproduce. It is a potential food source because it is high in protein and other essential nutrients; when dried, it is about 45% protein.