Solution

Autotrophic bacteria synthesize their cell constituents using carbon dioxide as the carbon source.
From the list, autotrophic bacteria include a total of six as Chara, Nostoc, Porphyra, Wolfia, Nitrosomonas, Nitrobacter. Of these Chara, Nostoc, Porphyra, Wolfia is photoautotrophs while Nitrosomonas, Nitrobacter are chemoautotrophs.
The other four (Lactobacillus, Streptomyces, Saccharomyces, Trypanosoma) are heterotrophs meaning they utilize organic compounds as a source of food.

Thus, the correct answer is option B.