The compound that would be a reactant in this process is A) Carbon Dioxide.
In the process of photosynthesis, plants utilize carbon dioxide (CO2) as a reactant. This process occurs in the chloroplasts of plant cells, where chlorophyll absorbs light energy, converting carbon dioxide and water into glucose and oxygen through a series of chemical reactions.
Chlorophyll, while crucial for capturing light energy, is not a direct reactant in this process. Glucose is a product of photosynthesis, and lactic acid is associated with fermentation in some organisms, not in the photosynthetic process.
Therefore, in the given options, the compound that serves as a reactant in the process described is A) Carbon Dioxide.