The biogas commonly used as a fuel for cooking is mainly a mixture of which two gases?

Introduction / Context:
This question is about renewable energy and environmental chemistry. Biogas is a fuel produced from the anaerobic decomposition of organic matter such as animal dung, plant waste and sewage. It is widely used in rural areas as a clean cooking fuel. Understanding its composition helps explain its energy content, combustion behaviour and environmental impact.

Given Data / Assumptions:

• The fuel in question is biogas used for cooking.
• Options list combinations such as carbon dioxide with oxygen, isobutane with propane, methane with carbon monoxide, methane with carbon dioxide and ethane with hydrogen.
• We assume standard descriptions of biogas composition.
• Biogas is produced in biogas plants under anaerobic conditions.

Concept / Approach:
Biogas typically contains about 50–70 percent methane (CH4), which is the main combustible component, and 30–50 percent carbon dioxide (CO2), with small amounts of hydrogen sulfide, water vapour and other gases. Methane provides the energy when biogas is burned, similar to natural gas. Carbon dioxide is non combustible but is produced as a by product in the digestion process and dilutes the fuel. Other options, such as mixtures of isobutane and propane or ethane and hydrogen, correspond more to liquefied petroleum gas or industrial mixtures rather than biogas. Carbon monoxide may be present only in traces, not as a major component of biogas used for cooking.

Step-by-Step Solution:
Step 1: Recall that biogas is produced by anaerobic digestion of organic waste by bacteria in a biogas plant. Step 2: The main gas produced in this process is methane, which is the primary energy carrier. Step 3: Carbon dioxide is also produced in significant amounts and forms the second largest component of biogas. Step 4: Other gases such as hydrogen sulfide and nitrogen may be present in small quantities but are not the primary components. Step 5: Therefore, biogas used for cooking is best described as a mixture of methane and carbon dioxide. Step 6: Compare this with LPG (liquefied petroleum gas), which mainly contains propane and butane, not methane and carbon dioxide. Step 7: Carbon monoxide is a toxic gas and is not a major intentional component of biogas mixtures used in households.

Verification / Alternative check:
Information from renewable energy resources and environmental science texts lists typical biogas composition as around 60 percent methane and 40 percent carbon dioxide, with minor fractions of other gases. This composition explains why biogas burns with a bluish flame and produces less soot than solid fuels, while also having a lower calorific value compared with pure methane or natural gas due to the diluting effect of carbon dioxide. Biogas digesters are designed to capture and use this methane rich gas for cooking and lighting, reducing reliance on wood and fossil fuels and lowering greenhouse gas emissions compared with uncontrolled decomposition.

Why Other Options Are Wrong:
Carbon dioxide and oxygen would be a mixture more similar to air enriched with CO2 but would not be a combustible fuel. Isobutane and propane are components of LPG, not biogas. Methane and carbon monoxide together describe producer gas or other industrial mixtures, but not standard biogas composition, and carbon monoxide is highly toxic. Ethane and hydrogen are not the main components of biogas; ethane is more associated with natural gas composition. Thus, these options do not match the well established composition of biogas used for cooking.

Common Pitfalls:
A frequent mistake is to confuse biogas with LPG or natural gas and therefore choose options containing propane or butane. Another error is to assume that carbon monoxide is a major combustible component, since it can burn; however, it is not produced in large amounts in typical biogas digesters and is highly poisonous. To avoid confusion, remember that biogas comes from biological digestion and is dominated by methane and carbon dioxide, while LPG is a petroleum product primarily containing propane and butane.

Final Answer:
Biogas used for cooking is mainly a mixture of methane and carbon dioxide.