By which process does carbon dioxide enter a plant?

Photosynthesis

Explanation:

Plants get the carbon dioxide they need from the air through their leaves. It moves by diffusion through small holes in the underside of the leaf called stomata . Guard cells control the size of the stomata so that the leaf does not lose too much water in hot, windy or dry conditions.

what are the options?

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.