Final answer:
The most stable isotope of Phosphorus is phosphorus-31, with a 1:1 neutron-to-proton ratio. It is the only stable and naturally occurring isotope of phosphorus, whereas other isotopes range from P-20 to P-47 and are radioactive.
Step-by-step explanation:
The most stable isotope of Phosphorus is phosphorus-31. This is because phosphorus-31 has 15 neutrons and 15 protons, which gives it a neutron-to-proton ratio of 1:1. Despite having an odd number of both neutrons and protons, which typically leads to instability, it is the most stable isotope of phosphorus, as it is the only phosphorus isotope that exists naturally and is stable. In contrast, isotopes with even numbers of both neutrons and protons tend to be more stable, with certain 'magic numbers' of neutrons or protons conferring additional stability. The stability of an isotope is influenced by these factors, along with its abundance in nature.
For example, when talking about atomic mass, elements such as technetium and promethium have all their isotopes radioactive and are not found naturally. Unlike these, phosphorus has a stable isotope, phosphorus-31, which predominates naturally similar to how hydrogen-1 and oxygen-16 dominate their respective elements.