Here's why:

* Solution: A homogeneous mixture of two or more substances.

* Solute: The substance that dissolves in the solvent.

* Solvent: The substance that dissolves the solute.

The expression "grams of solute per milliliters of solvent" would only describe the concentration of the solute in the solvent *before* it's mixed to form the solution. Once the solute dissolves, the resulting mixture is the solution, and the volume is no longer just that of the solvent.

Therefore, the correct way to express concentration in terms of grams and milliliters is:

grams of solute per milliliters of solution

This is often represented as g/mL.