Answer:
Atomic number
Explanation:
For the chemical specie, Z is the atomic number of atom shown.
Usually with most elements;
ᵃₙX
X is the symbol of the element
a is the atomic mass or mass number
n is the atomic number
In this problem, A is the atomic mass
Z is the atomic number
Atomic mass is the number of protons and neutrons
Atomic number is the number of protons.
