The unit for expressing the carbon dioxide concentration in the atmosphere is ppm. It refers to

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The question asks: The unit for expressing the carbon dioxide concentration in the atmosphere is ppm. It refers to

- The provided answer option is: d. molecules per million in a certain volume

To analyze, we first clarify what ppm represents in atmospheric science. Ppm stands for parts per million and is used to express extremely dilute concentrations. In the context of gases, ppm is commonly understood as a ratio of the number of CO2 molecules to the total number of molecules in a given volume of air, effectively a count of molecules per million molecules. This aligns with the intuitive idea of measuring how many CO2 molecules exist per one million molecules of the atmosphere sample, which is a volume-based way to express a molar or volumetric fraction in gases that mix uniformly.

Now, why this interpretation makes sense: in a gas mixture, the composition by volume (or by mole) is proportional to the number of particles present. Expressing concentration as ppm therefore conveys the proportion of CO2 molecules among all atmospheric molecules, scaled to one million molecules. This framing is widely used because it remains meaningful across varying total pressures and temperatures, as long as the mixture is الغازية (gas-like) and well-mixed.

Assuming there were other options, we would evaluate them similarly:
- If an option claimed ppm is a simple percentage, that would be inaccurate because ppm is not a percent unless explicitly converted (1% = 10,000 ppm).
- If an option suggested ppm measures mass per mass (ppm by mass), that would be incorrect in atmospheric chemistry where ppm typically denotes a mole or volume fraction, not a mass ratio.
- If an option asserted ppm refers to time units or energy units, that would be a clear misrepresentation of what ppm measures in this context.

In summary, the statement described in the provided option corresponds to the conventional meaning of ppm in atmospheric science: a ratio expressed as molecules per million in a given volume of air, reflecting the proportion of CO2 among all atmospheric molecules.

Dashboard QUIZ Multiple choice questions - Part 1

The unit for expressing the carbon dioxide concentration in the atmosphere is ppm. It refers to

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