The correct options are
B Methanogens in the cow dung are the source of methane and hydrogen gas.
C Anaerobic bacteria such as Methanobrevibacter and Methanomicrobium are responsible for the production of biogas
Biogas is primarily obtained from cow dung in India. Cow dung is rich in methanogens. It is converted into a slurry by mixing with water and is allowed to decompose and get digested by anaerobic bacteria. This produces gases such as methane and hydrogen. After production of biogas, the leftover solid waste is used as manure, since it is rich in organic nutrients.