What are the main constituents of biogas?

Biogas is a renewable energy source produced through the anaerobic digestion of organic matter such as animal waste, shrubs, and farm waste [1]. The primary constituents of biogas are methane (CH4) and carbon dioxide (CO2) [3]. Methane typically accounts for 50% to 75% of the mixture, while carbon dioxide makes up approximately 25% to 50% [1]. Together, these two gases constitute about 95% of the total biogas volume. While trace amounts of other gases like hydrogen sulfide (H2S), nitrogen, hydrogen, and water vapor may be present depending on the feedstock, methane and carbon dioxide remain the dominant components [1]. Methane is the key energy-containing constituent, making biogas a viable fuel for heating and electricity generation [3]. Other options involving sulfur dioxide or nitric oxide are incorrect as these are not primary constituents of raw biogas.

Sources

1. [1] https://www.epa.gov/agstar/how-does-anaerobic-digestion-work
2. [3] Science , class X (NCERT 2025 ed.) > Chapter 4: Carbon and its Compounds > 4.1 BONDING IN CARBON – THE COVALENT BOND > p. 60