Which one of the following gas is not the component of biogas?

The correct answer is Option (2) → Carbon monoxide

Biogas is a mixture of gases that microbes make while they digest organic matter without oxygen, in sewage sludge or in a biogas plant. Methane is the main gas, and the mixture can be burnt as fuel.

(1) Hydrogen sulphide — A component of biogas. It is one of the gases that the bacteria release along with methane.

(2) Carbon monoxide — Not a component of biogas. The anaerobic bacteria do not make it.

(3) Carbon dioxide — A component of biogas. It is a normal product of the microbial digestion.

(4) Methane — A component of biogas. It is made by methanogens, and it is the main fuel gas in biogas.

Note: A similar question was also asked in CUET (UG) 2026 on 06-06-2026 (Slot 1) and on 26-05-2026 (Slot 1).

NCERT Extract:
Microbes in Sewage Treatment – “… The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters. Here, other kinds of bacteria, which grow anaerobically, digest the bacteria and the fungi in the sludge. During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases form biogas and can be used as source of energy as it is inflammable.”