Which of the following gases form biogas?
A. CH4
B. CO2
C. H2S
D. O2
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A, B and C only
Biogas is a mixture of gases made when bacteria break down organic matter without oxygen (anaerobic digestion).
(A) CH4 — Correct. Methane is the main gas of biogas.
(B) CO2 — Correct. Carbon dioxide is also produced.
(C) H2S — Correct. Hydrogen sulphide is also produced.
(D) O2 — Incorrect. Biogas is made in the absence of oxygen, so oxygen is not one of its gases.
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.”