Which one of the following statements is NOT correct?

Biomass is a renewable energy source derived from organic materials like farm and animal waste [1][5]. Biogas (Gobar gas) is produced through the anaerobic decomposition of substrates such as cow dung, crop residues, and sewage in the absence of oxygen [1][4]. This process reduces soil and water pollution by managing organic waste that would otherwise contaminate surface waters or landfills [4]. Regarding heating capacity, biogas is highly efficient for domestic use, offering higher thermal efficiency than kerosene, dung cakes, or charcoal [1]. While raw biogas has a lower calorific value (4,800–6,900 kcal/m3) compared to pure methane or LPG due to carbon dioxide content, it is not considered 'very low' in a functional context; it is an effective fuel for cooking, heating, and power generation. Therefore, statement 4 is the least accurate as it overlooks the gas's high thermal efficiency and utility.

Sources

1. [1] NCERT. (2022). Contemporary India II: Textbook in Geography for Class X (Revised ed.). NCERT. > Chapter 5: Print Culture and the Modern World > Biogas > p. 117
2. [5] https://www.fao.org/4/t0541e/t0541e0b.htm
3. [4] https://pmc.ncbi.nlm.nih.gov/articles/PMC11636105/