Which hydrocarbon is a gas at normal temperature and pressure?

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Multiple Choice

Which hydrocarbon is a gas at normal temperature and pressure?

The key idea is how boiling point determines a substance’s phase at a given temperature. For alkanes, boiling points rise as the carbon chain length increases, but all of the four listed have boiling points well below typical room temperature (about 25°C). Methane boils at -161°C, ethane at -88°C, propane at -42°C, and butane at around -0.5°C. Since room temperature is far above these values, each of these hydrocarbons exists as a gas under normal temperature and pressure. So, all four are gases at room conditions; there isn’t a single one that uniquely fits the criterion.

The key idea is how boiling point determines a substance’s phase at a given temperature. For alkanes, boiling points rise as the carbon chain length increases, but all of the four listed have boiling points well below typical room temperature (about 25°C). Methane boils at -161°C, ethane at -88°C, propane at -42°C, and butane at around -0.5°C. Since room temperature is far above these values, each of these hydrocarbons exists as a gas under normal temperature and pressure. So, all four are gases at room conditions; there isn’t a single one that uniquely fits the criterion.

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