The term that would describe the contents would be the volume of the cylindrical container. From the definition of matter, gases do not have a definite shape and volume. It takes the shape and volume of their container. So, if you want to know how much Nitrogen Oxide there is in the container, you have to determine the volume of the cylinder.
Three hundred and ten million, seven hundred sixty-three thousand, one hundred and thirty-six
1-(28-21)/28=.075
Answer is D