Protists use all of the following methods to obtain energy except A. photosynthesis / B. ingesting food / C. converting atmospheric nitrogen / D. absorbing food.

Algae, which are protists, can obtain energy through photosynthesis. Protists which primarily obtain food in heterotrophic methods such as ingesting and absorbing for nutrition. However, protists cannot obtain food through nitrogen fixation since all nitrogen fixers are prokaryotic and protists are eukaryotic organisms.

Protists consist of various types of organisms. They can either be autotrophs or heterotrophs. Autotrophs meaning, they can produce their own source of energy through the process of photosynthesis. Heterotrophs, when they obtain their energy through ingestion or absorption from other sources. So in the given question, the method of energy that protists do not do is option C. converting atmospheric nitrogen.