We’re asked to give the nuclear symbol for the isotope of phosphorus for which A = 31.
Recall that the symbol for an element or ion is as follows:
The nuclear symbol for isotopes is also written in the same manner.
From the periodic table, we can see that the atomic number of Phosphorus, P is 15 (Z = 15).
Recall that A stands for the atomic mass or mass number. We’re given the mass number, A = 31.