The correct answer is A) Green. Nonflammable gases should have a green label, as per the US Department of Transportation (DOT) hazardous materials regulations. The green label signifies that the gas is not flammable, which is an important safety consideration for transportation and storage. The other answer choices are incorrect because white is for non-hazardous materials, red is for flammable materials, and the skull and crossbones is for poison/toxic materials, none of which accurately describe the hazard class of nonflammable gases.