B. Copper turning green in the air.
A physical change is a change that changes the characteristics of something without creating a new substance
When the iron rusts under water it creates a new substance which is rust so it wouldn’t be this one.
The liquid nitrogen changed into nitrogen gas which is a new substance so it would be this one.
And the sodium and chlorine produces a new substance (sodium chloride) so it wouldn’t be this one.
When the copper turned green it did not create a new substance it simply changed the color of the copper so it would be this one.
