Which is a chemical property of copper? a. has a boiling point of 2567° c b. reacts in air to form a green layer c. has the symbol cu d. is a solid at room temperature?

The answer should be B, it reacts in air to form a green layer.

Chemical properties means that how the substance that reacts with other substance to produce new substances. Usually it cannot be measured or observed just with the substance itself.

From all the options above, only B is a reaction. The green layer formed is a new substance produced by copper and air. It involves a chemical change.

Other options like boiling points or state of matter, these are physical properties. They do not require it to react to other substances and the can be measured and observed easily.

Gases undergo changes in volume most easily.  

Hope this helps :)