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

The correct answer is Option (3) → Carbon monoxide

Biogas is a mixture of gases produced by microbes and is used as a fuel. Methanogens such as Methanobacterium grow without oxygen on cellulose-rich matter like cattle dung and sewage sludge. They produce mainly methane, along with carbon dioxide and hydrogen. The biogas formed in the sludge digesters of sewage treatment plants also contains hydrogen sulphide.

(1) Methane — A component of biogas. It is the main gas and the one that burns.

(2) Carbon dioxide — A component of biogas.

(3) Carbon monoxide — Not a component of biogas. Carbon monoxide is a poisonous gas formed when fuel burns in too little oxygen, as in vehicle exhaust. Methanogens do not produce it.

(4) Hydrogen sulphide — A component of biogas. It is formed in the anaerobic sludge digesters during sewage treatment.

Note: A similar question was also asked in CUET (UG) 2026 on 30-05-2026 (Slot 2) 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.”