What type of socket should be used with an air impact wrench
a. black
b. chrome.
c. 12 point
d. either a or b?

Black sockets should be used, but the color is not the reason why. Chrome sockets will cause splits to form in the socket walls pretty quickly, after only a few uses. But the black sockets are that color because they have gone through a process called Parkerizing that coats the surface of the socket in order to provide more resistance when being used and protect the socket against corrosion.