The sum of protons plus neutrons is the mass number.
We designate a specific group of atoms by using the term "nuclide." A nuclide refers to a group of atoms with specified atomic number and mass number.
The ratio of calcium formed to argon formed is fixed and known.Strontium-86 is a stable element that does not undergo radioactive change.In addition, it is not formed as the result of a radioactive decay process.(Creationists claim that argon escape renders age determinations invalid.However, any escaping argon gas would lead to a determined age younger, not older, than actual.