Final answer:
A lipid-soluble molecule is most likely to serve as an ionophore because it can dissolve in a cell's lipid bilayer, allowing it to transport ions across the membrane which is typically impermeable to ions.
Step-by-step explanation:
The question asks which of the given options could most likely serve as an ionophore. An ionophore is a substance that can transport ions across the lipid membrane of a cell, which is generally not permeable to ions due to the hydrophobic nature of the lipid bilayer. Considering the options, a lipid-soluble molecule is the most likely to serve as an ionophore because it can dissolve in the lipid bilayer and facilitate the passage of ions.
Water is a polar molecule and is not lipid-soluble, sodium chloride (NaCl) is an ionic compound and also not lipid-soluble, while a strong acid generally refers to the ability to dissociate completely in water, which does not indicate the ability to transport ions across lipid membranes. Therefore, the correct option is c) A lipid-soluble molecule.