Hey Parbhat

The void ratio of a mixture is the ratio of the volume of voids to volume of solids.Dry density of a soil is the ratio of total drymass of soil to the total volume of soil. dry density is related to the degree of compaction of soil mass.

So on having the equation and graph in between these two it gives us a result as increase of dry density means a decrease of voids ratio and a more compact soil.