Explanation:

Biogas mainly comprises of three main gases. It is a mixture of methane, hydrogen, and carbon dioxide. It can be produced by agricultural waste, food waste, animal dung, manure, and sewage. The process of biogas production is also known as anaerobic digestion. Biogas is typically a gas evolved by the biological breakdown of organic wastes in absence of O2 . It is used as biofuel and made up basically of CH4 (50-75%), CO2 (25-50%) N2 (0 -10%), H2 (0-1%), H2s (0-3%) and O2 (0-1%). Hence option 2nd is correct.