Ammonia R-717 is classified by its toxicity and flammability as a:

Ammonia R-717 is classified as a Group two refrigerant due to its specific characteristics concerning toxicity and flammability. Group two refrigerants have a significant level of toxicity and present a potential hazard if not handled correctly. R-717 is particularly known for being toxic in high concentrations, and proper safety measures must be taken when working with it.

In contrast, other classifications such as R1 or ANSI 7 don't correspond to the same set of guidelines regarding toxicity or flammability. R1, for instance, typically includes refrigerants that don't pose a high toxicity risk. ANSI 7 references standards set by the American National Standards Institute, which does not directly relate to the classifications of refrigerants concerning their safety attributes.

Thus, by understanding that ammonia's characteristics align with a significant danger due to toxicity, it is clearly identified as a Group two refrigerant, highlighting the importance of safety training and precautions in handling it.