The correct option is B Sargassum
Many species of Porphyra, Laminaria and Sargassum are among the 70 species of marine algae used as food.Volvox is the colonial algae which is not an edible alga, although not poisonous. Agar, one of the commercial products, is obtained from Gelidium. Spirulina is an edible single cell protein but they are cyanobacteria and not algae.