In energy resources, biogas from anaerobic digestion and natural gas from fossil fuel deposits both contain one main combustible component. Which gas is this primary component?

Introduction / Context:
Biogas and natural gas are both important energy sources. Biogas is produced from the decomposition of organic matter in the absence of oxygen, while natural gas is obtained from underground fossil fuel deposits. Both gases are mixtures of several components but have one main fuel gas in common. This question asks you to identify that main component.

Given Data / Assumptions:

• Biogas comes from anaerobic digestion of organic waste in biogas plants.
• Natural gas is extracted from gas fields and is widely used in homes and industries.
• The options list carbon dioxide, butane, hydrogen sulphide, and methane.
• We assume standard compositions described in school level science books.

Concept / Approach:
Methane (CH4) is the principal component of both biogas and natural gas. In biogas, methane content is often around 55 to 70 percent, with carbon dioxide making up most of the remainder and small amounts of other gases. Natural gas typically contains more than 80 or 90 percent methane, with small quantities of ethane, propane, and other hydrocarbons. Carbon dioxide and hydrogen sulphide are unwanted impurities in these mixtures, and butane is mainly associated with liquefied petroleum gas, not as the main component of biogas or natural gas. Therefore, methane is the correct answer.

Step-by-Step Solution:

Verification / Alternative check:
Energy and environmental science books describe natural gas as composed mainly of methane, with smaller amounts of ethane and other hydrocarbons. Biogas composition charts show methane as the majority combustible gas with carbon dioxide as the main non combustible fraction. Technical guides on biogas production emphasise increasing methane content to improve fuel quality, confirming that methane is the main component in both cases.

Why Other Options Are Wrong:

• Carbon dioxide is wrong because it does not burn and is more of a diluting gas in biogas.
• Butane is wrong because it is important in liquefied petroleum gas, not as the main substance in natural gas or biogas.
• Hydrogen sulphide is wrong because it is an impurity that must be removed due to toxicity and corrosive nature, not the main fuel gas.

Common Pitfalls:
Some learners confuse natural gas with liquefied petroleum gas and think of butane or propane first. It is helpful to remember that natural gas equals methane dominated, while LPG equals propane and butane dominated. Biogas produced in rural plants also has methane as its main useful component.

Final Answer:
Methane, a simple hydrocarbon gas used as fuel