Final answer:
The best time to purge an ammonia plant containing 250 lbs. of ammonia is during a shutdown to minimize safety risks and the loss of ammonia. Nitrogen fixation is the process of converting nitrogen gas into ammonia but is not related to the purging of an ammonia plant. So the correct answer is option (A).
Step-by-step explanation:
The question is asking about the best time to purge an ammonia plant that contains 250 lbs. of ammonia. Purging an ammonia plant essentially means removing unwanted contaminants and ammonia itself from the system in a controlled and safe manner. This is important to maintain the efficiency and safety of plant operations.
When referring to the safety and stability of storing ammonia, as well as minimizing the loss of ammonia, the optimal time to purge an ammonia plant would typically be during shutdown. This is due to the fact that during a shutdown, the plant is not in operation, which minimizes risks associated with handling ammonia and allows for a more controlled purging process. Additionally, with the plant not in operation, there's less risk of releasing ammonia into areas where it could be hazardous to both personnel and the environment.
The conversion of nitrogen gas (N2) into ammonia (NH3) is known as nitrogen fixation, which is a separate process from purging an ammonia plant but relevant to understanding the chemical processes involving ammonia.