The correct unit of measure for density is C) grams per milliliter (g/mL). Density is defined as mass per unit volume, so the formula for density is usually expressed as:
\[ \text{Density} = \frac{\text{Mass}}{\text{Volume}} \]
In the metric system, mass can be measured in grams (g) and volume in milliliters (mL), leading to the unit of grams per milliliter (g/mL).