What percentage of carbon dioxide is present in dry air?

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Study for the IGCSE Edexcel Chemistry Test. Access flashcards and multiple choice questions with hints and explanations. Get ready for your exam!

Multiple Choice

What percentage of carbon dioxide is present in dry air?

Explanation:
The key idea is that carbon dioxide is a trace gas in the atmosphere. In dry air, CO2 makes up only a very small fraction, about 0.04% by volume, which is roughly 400 parts per million. This is tiny next to the major components: nitrogen about 78% and oxygen about 21%. So 0.04% is the correct amount for CO2 in dry air. The other numbers represent the main gases (78% and 21%), not CO2, and a much larger percentage like 0.9% would imply far more CO2 than is actually present in Earth's atmosphere.

The key idea is that carbon dioxide is a trace gas in the atmosphere. In dry air, CO2 makes up only a very small fraction, about 0.04% by volume, which is roughly 400 parts per million. This is tiny next to the major components: nitrogen about 78% and oxygen about 21%. So 0.04% is the correct amount for CO2 in dry air. The other numbers represent the main gases (78% and 21%), not CO2, and a much larger percentage like 0.9% would imply far more CO2 than is actually present in Earth's atmosphere.

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