Which of the following is a synonym for Anhydrous Ammonia?

Anhydrous ammonia is a term that specifically refers to ammonia (NH3) that does not contain any water, making it a concentrated form of this compound. Ammonia is widely recognized in various industrial applications, particularly in refrigeration systems, where it serves as a refrigerant due to its favorable thermodynamic properties.

While the other terms listed relate to different chemical substances, they do not accurately represent or synonymize with anhydrous ammonia. For instance, amines are organic compounds derived from ammonia, methane is a simple hydrocarbon, and hydrogen is a fundamental element that exists in various compounds but does not represent ammonia itself. Thus, selecting ammonia as the synonym for anhydrous ammonia is correct, as it directly reflects the same chemical identity without the presence of water.