Density is the mass per unit volume.
Common units for density are g/cm3 or kg/m3. SI unit is kg/m3.
Density of a pure substance is fixed, regardless of it’s size!
Floating and Sinking
A denser (heavier) substance will sink in liquid which is less denser (lighter).
A less dense substance will float in a liquid which is denser.
If substance has the same density as the liquid, it will be suspended in the liquid.