Final answer:
A substance with a density of 1.2 g/mL will sink in water since its density is greater than the water's density of 1.00 g/mL.
Step-by-step explanation:
If a substance's density is 1.2 g/mL, which is greater than the density of water at 1.00 g/mL, it will sink in the water. This is because objects with a density greater than that of the liquid they are in will sink. Conversely, objects with a lower density than the liquid will float. This principle is based on the relative density or specific gravity of the object in comparison to the liquid.
Understanding the relationship between the density of a substance and its buoyancy in a liquid is crucial for predicting whether an object will sink or float. In the case where a substance has a density of 1.2 g/mL, surpassing the density of water (1.00 g/mL), the substance will indeed sink when placed in water.