Final answer:
The correct answer is D) The density changed. When the volume of nitrogen increases while the mass remains the same, the density decreases. This is a physical change affecting a physical property of the substance, without altering its chemical composition.
Step-by-step explanation:
When an amount of nitrogen undergoes a physical change and increases its volume, what can be known about this physical change is that D) The density changed.
A physical change occurs when the physical properties of a substance change, but its chemical identity remains the same. In this case, if the volume of nitrogen increases, assuming the mass remains constant, the density would decrease because density is a measure of mass per unit of volume. Since this is a change in a physical property, without any evidence of a chemical reaction or change in chemical composition, it can be classified as a physical change.
Examples of other physical changes include the melting of ice or the boiling of water, both of which involve a change in state but not a change in the chemical composition of the substance.