Final answer:
Maximum photosynthesis occurs in the palisade mesophyll of a green leaf, which is rich in chloroplasts and is the primary site for this process.
Step-by-step explanation:
In the context of photosynthesis, maximum activity occurs in the palisade mesophyll of a green leaf. The palisade mesophyll consists of column-shaped, tightly packed cells and is typically located below the upper epidermis and above the spongy mesophyll. This layer is rich in chloroplasts, which are necessary for the photosynthetic process. While guard cells do contain chloroplasts, they are not the primary site of photosynthesis. Thus, the correct answer to which part of the leaf has the maximum photosynthesis occurring is c) Palisade mesophyll.