Bacteria that use chemicals like sulfur as an energy source are considered
a. photoautotrophs.
b. heterotrophs.
c. saprobes.
d. chemoautotrophs.

Bacteria that use chemicals like sulfur as an energy source are considered as chemoautotrophs. Chemoautotrophs are the organism that derives energy and from inorganic substances such as sulfur, ammonia etc. These organisms are most commonly found in extreme and hostile environments such as the deep sea vents where there is not enough sunlight and hence the primary producers (chemoautotrophs) depends on the inorganic energy sources.An example of such bacteria is Paracoccus.

Photosynthesisthe process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water.