Question

Given below are two statements :
Statement (I): Biogas is a mixture of $\text{CH}_4$, $\text{CO}_2$ and $\text{H}_2$.
Statement (II): Biogas is produced by aerobic digestion of organic waste material.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are false.
• B. Both Statement (I) and Statement (II) are true.
• C. Statement (I) is true but Statement (II) is false.
• D. Statement (I) is false but Statement (II) is true.

Hint:

Anaerobic digestion of organic waste proceeds through four sequential stages: Hydrolysis $\rightarrow$ Acidogenesis $\rightarrow$ Acetogenesis $\rightarrow$ Methanogenesis.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Biogas is a renewable biofuel produced by the microbial breakdown of organic matter.
This decomposition process requires specific groups of microorganisms operating under strict environmental conditions.

Step 2: Detailed Explanation:
Let us evaluate both statements:
- Statement (I): Biogas is a gaseous fuel mixture.
Its primary components are methane ($\text{CH}_4$, typically $50-75\%$) and carbon dioxide ($\text{CO}_2$, typically $25-50\%$), along with trace amounts of nitrogen, hydrogen ($\text{H}_2$), and hydrogen sulfide ($\text{H}_2\text{S}$).
Thus, Statement (I) is true.
- Statement (II): Biogas is produced through anaerobic digestion (in the complete absence of molecular oxygen), not aerobic digestion.
The final stage of biogas production, methanogenesis, is carried out by methanogenic archaea, which are obligate anaerobes.
Oxygen is toxic to these organisms and halts biogas production.
Therefore, Statement (II) is false.

Step 3: Final Answer:
Statement (I) is true, but Statement (II) is false, corresponding to option (C).