What gas do plants absorb from the atmosphere?

Plants absorb carbon dioxide from the atmosphere through tiny openings in their leaves called stomata. This gas is a crucial component of the process known as photosynthesis, where plants use sunlight to convert carbon dioxide and water into glucose (a sugar) and oxygen. During this process, carbon dioxide is essential as it provides the carbon needed for the formation of organic compounds that make up plant biomass.

Oxygen, while a product of photosynthesis and necessary for respiration in animals, is not absorbed by plants in the same way carbon dioxide is. Hydrogen, on the other hand, is found in water molecules and is part of the photosynthesis process but is not an atmospheric gas that plants absorb. Nitrogen, though abundant in the atmosphere and important for plant growth, is primarily absorbed in the form of nitrates from the soil rather than directly from the air. Thus, the absorption of carbon dioxide is key to plants' ability to produce their food and is what makes option C the correct answer.