Final answer:
When marked with 'NH3', the content of a purger is A) Ammonia gas, as ammonia is a compound of nitrogen and hydrogen used in many industrial applications and also as a refrigerant gas.
Step-by-step explanation:
In the context of the question with the symbol 'NH3' mentioned, the term 'purger' hints at the presence of a substance that is being removed or 'purged' from a system. Considering the options provided, one could determine the content of the purger by understanding the properties of ammonia (NH3). Ammonia is a compound of nitrogen and hydrogen that is often used in household cleaners, and it is a colorless gas with a characteristic sharp, pungent smell. It is widely used in industry, particularly in the production of fertilizers, and it can also be used as a refrigerant gas.
The correct answer to what is in a purger when it is marked with 'NH3' is A) Ammonia gas. Purgers are often used in refrigeration and various industrial systems to remove unwanted gases. Since option A specifically mentions ammonia gas, we can conclude that the purger in question is designed to remove ammonia from a system.