Microbial Metabolism: Gases Released — NEET Biology

Correct answer: C — S1 and S2 only

The core concept here focuses on the precise composition of biogas and the conditions governing its production. S1: Biogas is predominantly methane. NCERT mentions methane, CO2, and H2 for biogas from cellulosic material, and methane, H2S, and CO2 from anaerobic sludge digestion. Thus, including hydrogen and hydrogen sulphide along with methane and carbon dioxide provides a comprehensive description of biogas composition. This statement is correct. S2: Methanogens are anaerobes, meaning the absence of oxygen is essential for their metabolic activity and efficient methane production. This statement is correct. S3: Ethylene is not listed as a component of biogas produced by microbial activity in biogas plants. The primary gases are methane, CO2, and H2/H2S. Thus, this statement is incorrect. S4: NCERT explicitly states that the type of gas produced depends upon the microbes and the organic substrates they utilise. Thus, this statement is incorrect. S5: Biogas contains carbon dioxide, which is a non-flammable gas. Therefore, it does not generate only combustible gases. Thus, this statement is incorrect. Therefore, statements S1 and S2 are correct. Option A is incorrect because S3 is false. Option C is incorrect because S3, S4, and S5 are false. Option D is incorrect because S4 and S5 are false. Option B correctly identifies S1 and S2 as correct. The question tests detailed knowledge of biogas composition and the factors influencing its production.