Which gas is consumed by plants during photosynthesis?

• A. Oxygen
• B. Nitrogen
• C. Carbon dioxide
• D. Hydrogen

Answer: (C)

During photosynthesis, plants take in carbon dioxide from the air and use light energy to convert it into organic molecules like glucose. This gas serves as the carbon source that gets fixed into sugars, which is why carbon dioxide is consumed. The process also releases oxygen as a byproduct, not a fuel used up by the plant. The other gases listed aren’t part of this carbon-fixing step: nitrogen is used for building proteins and other molecules in ways that aren’t part of photosynthesis, and hydrogen isn’t taken up as a separate gas in this reaction (it mainly comes from water and becomes part of the new sugars and water).