Identify the correct statement regarding chemoautotrophs.
(a) These bacteria can manufacture their organic food from inorganic raw materials.
(b) The energy for food production is derived from exergonic chemical reactions involving oxidation of an inorganic substances in nature.
(c) Purple sulphur bacteria is a chemoautotroph.

They are bacteria which are able to manufacture their organic food from inorganic raw materials with the help of energy derived from exergonic chemical reactions involving oxidation of an inorganic substances in nature.
Example: Nitrifying bacteria, Sulphur oxidizing bacteria, Iron bacteria etc.
Purple sulphur bacteria are examples of phototrophs.