A nucleus can be read as a count ledger: mass number is the total of protons and neutrons, while proton number sets the element. The split is exact for the stated isotope model; real isotope identification relies on detector signals, mass measurements, and calibration chains with finite uncertainty.
A nucleus identity begins as an exact count ledger. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Mass number splits into proton and neutron counts
A training nucleus with mass number 14 and proton number 6 has neutron count 8.
14=6+8
The element label is the proton count
The proton count 6 identifies the element in this training ledger.