If a tempurature of a piece of steel decreases, what happens to its density

The density will increase

Explanation:

A decrease in temperature of the piece of steel will result in a decrease in its volume since cooling is associated with contraction and heating with expansion.

Density is defined as the mass per unit volume of a substance;

Density = mass/volume

A decrease in temperature does not affect the mass of any substance. Therefore, the mass remains constant but the volume is lowered. From the equation above this will imply that the density of the piece of steel will increase.

Density is inversely proportional to volume.