Parenchyma cells in the spongy mesophyll exhibit large intercellular spaces promoting:

The correct option is: Greater exposure to carbon dioxide.

Explanation:
The spongy mesophyll is a tissue layer located in the leaves of plants. It is composed of loosely arranged, irregularly shaped parenchyma cells.
The defining characteristic of this layer is the presence of large intercellular air spaces between the cells. These air spaces facilitate the rapid diffusion of gases (such as carbon dioxide, oxygen, and water vapor) throughout the leaf.
Since carbon dioxide (${\mathrm{CO}}_2$) is a vital reactant for photosynthesis, the loose arrangement of spongy parenchyma cells increases the surface area of the cell walls exposed to the internal air spaces. This design allows for a more efficient gas exchange, specifically promoting greater exposure of the cells to carbon dioxide, which can then dissolve into the cells and be utilized by chloroplasts during light-independent reactions of photosynthesis.