Which of the following compounds is used as a gaseous fuel?

Analysis of the Question

The question asks us to identify which of the given organic compounds is commonly used as a gaseous fuel. In chemistry, gaseous fuels are typically low-molecular-weight hydrocarbons (alkanes or alkenes) that are gases at room temperature and pressure.

Concept Explanation

• Physical State of Alkanes: In the homologous series of alkanes, the first four members ($C_1$ to $C_4$) are gases at room temperature. These include methane, ethane, propane, and butane.
• Fuel Properties: Because these short-chain hydrocarbons have low boiling points and burn cleanly with oxygen to release significant amounts of energy, they are widely used as fuels (e.g., LPG - Liquefied Petroleum Gas).
• Evaluating the Options: • Option A: This represents a carboxylic acid derivative. These are generally liquids or solids and are not used as gaseous fuels. • Option B: This is Propyne ($CH_3-C \equiv CH$). While it is a gas, it is primarily used in welding and cutting torches rather than as a standard domestic gaseous fuel. • Option C: This is Butane ($CH_3-CH_2-CH_2-CH_3$). Butane is a four-carbon alkane. It is a gas at room temperature and is a primary component of LPG, making it a standard gaseous fuel. • Option D: This structure is chemically incomplete/incorrect as written, but it does not represent a standard stable gaseous fuel molecule.

Step-by-Step Solution

1. Identify the chemical formulas: • A: Represents a complex organic acid structure. • B: Propyne ($C_3H_4$). • C: Butane ($C_4H_{10}$). • D: Incorrectly represented structure.
2. Determine the state: Butane ($C_4H_{10}$) is a gas at room temperature. It is highly flammable and is stored under pressure in cylinders for use as fuel in homes and industries. 3.

Conclusion

Butane is the correct answer because it is a gaseous alkane used extensively as a fuel source.

Exam Tip: Remember the "Gas Rule" for alkanes: $C_1$ to $C_4$ (Methane to Butane) are gases, $C_5$ to $C_{17}$ are liquids, and $C_{18}$ and above are solids. If you see a question about gaseous fuels, always look for the short-chain alkanes!