Density is defined as mass per unit volume. The density of water is 1.0 g/cm³. This means that for every cubic centimeter of water, there is 1 gram of mass. The density of the object is 2.1 g/cm³. This means that for every cubic centimeter of the object, there is 2.1 grams of mass.

Since the density of the object is greater than the density of water, the object will sink in water.