Question

a gas that plants take in (reactant) through small holes in their leaves for the process of photosynthesis. choose an answer oxygen carbon dioxide nitrogen carbon monoxide dont know?

Explanation:

Plants take in carbon dioxide ($CO_2$) through stomata (small holes in leaves) for photosynthesis. The chemical equation for photosynthesis is $6CO_2 + 6H_2O \xrightarrow{light} C_6H_{12}O_6+6O_2$. Oxygen is a product of photosynthesis. Nitrogen is mainly absorbed by plants from the soil in the form of nitrates, not directly as a gas for photosynthesis. Carbon monoxide is toxic to plants and not a reactant in photosynthesis.

Answer:

carbon dioxide