Final answer:
The group of bacteria primarily involved in oxidizing hydrocarbons is Proteobacteria, which are Gram-negative bacteria with diverse metabolic abilities, including the degradation of hydrocarbons. Option b is correct.
Step-by-step explanation:
The group of bacteria primarily involved in oxidizing hydrocarbons is Proteobacteria. These bacteria, particularly the class of Gamma-proteobacteria, contain many species that can metabolize hydrocarbons. They are Gram-negative bacteria, which are known for their diverse metabolic capacities, including the ability to degrade various organic pollutants.
Although other groups like Cyanobacteria and Archaea have significant ecological roles, such as oxygen production and methanogenesis respectively, Proteobacteria are more associated with hydrocarbon oxidation processes. Cyanobacteria, for example, are primarily known for their photosynthetic abilities and were crucial in oxygenating the earth's atmosphere ages ago. Meanwhile, Archaea, which includes methanogens, are more associated with processes like anaerobic respiration using CO2 to produce methane, rather than hydrocarbon oxidation.