What gas do plants absorb from the atmosphere?

Plants absorb carbon dioxide from the atmosphere for the process of photosynthesis. During photosynthesis, plants take in carbon dioxide through small openings in their leaves called stomata. They use sunlight to convert this carbon dioxide, along with water taken up from the soil, into glucose (a type of sugar) and oxygen. The glucose provides energy for the plant, while the oxygen is released back into the atmosphere as a byproduct.

The other gases listed—oxygen, nitrogen, and hydrogen—do not serve the same essential role for plants. Oxygen is a byproduct of photosynthesis and is released, nitrogen is more involved in the soil and is utilized by plants in different forms, while hydrogen is primarily found in water and is not absorbed directly from the atmosphere.