The major constituent of biogas is methane. Biogas is a type of renewable energy that is produced through the breakdown of organic materials such as plant and animal waste in the absence of oxygen. Methane is the main component of biogas, typically making up 50-75% of its composition.
Option 1: Carbon dioxide is a minor component of biogas, usually comprising around 25-50% of its composition. It is produced during the anaerobic digestion process along with methane.
Option 2: Nitrous oxide is not a major constituent of biogas. It is a greenhouse gas that is produced through various agricultural and industrial activities.
Option 4: Oxygen is not a constituent of biogas. Biogas is produced in the absence of oxygen, in a process called anaerobic digestion.
Overall, option 3 is the correct answer as methane is the primary component of biogas, while options 1, 2, and 4 are not major constituents of biogas.