What do we mean by density? A. Density is used to describe compactness or crowding. B. Density is used to describe how much liquid is in a container. C. Density is used to describe the area on a surface. OD. Density is used to describe how thick a liquid is. What do we mean by concentration? OA. Concentration is used to describe how hot or cold a substance is. OB. Concentration is used to describe the amount of one substance that is mixed with another. OC. Concentration is used to describe how thick a liquid is. OD. Concentration is used to describe how fast a substance is changing in volume.