Acork is able to float on water because it is a: a crystalline sold b: equal density to water c: small in size d: less dense than the water

D.Less dense than water. Cork has a density of 0.24g/cm³. Water has a density of about 1g/cm³. 

Another example:  Ice floats in water because the density of ice is less than the density of water( 1g/cm³). Ice has a density of 0.92 g/cm³.