Final answer:
In sodium chloride dissolution illustrations, red molecules often symbolize the oxygen atoms in water molecules that form a hydration shell around the sodium ions.
Step-by-step explanation:
In the illustration with red and white molecules, when sodium chloride is involved, the red molecules typically represent the oxygen atoms of water molecules in the hydration shell that surrounds the ions after dissolving. Since sodium ions (Na+) are surrounded by water molecules with oxygen atoms oriented near the positive ion, it would be plausible that in the provided context, the red molecules illustrate the oxygen atoms of the water molecules that are part of the hydration shell around the positively charged sodium ions.