Question

name that gas that is a reactant (input) of photosynthesis. water vapor carbon dioxide helium oxygen

Explanation:

Photosynthesis is the process by which plants use sunlight to convert carbon dioxide ($CO_2$) and water ($H_2O$) into glucose ($C_6H_{12}O_6$) and oxygen ($O_2$). The chemical equation for photosynthesis is:

$$6CO_2 + 6H_2O+light\ energy ightarrow C_6H_{12}O_6 + 6O_2$$

. Among the options, water vapor is in liquid - gas equilibrium and not the gaseous reactant in the typical sense of the photosynthesis equation written with gas - phase reactants. Helium is an inert gas and not involved in photosynthesis. Oxygen is a product of photosynthesis. Carbon dioxide is the gas that is taken in by plants (along with water) as a reactant for photosynthesis.

Answer:

carbon dioxide