Answer:
B. Atomic number from mass number
Explanation:
The general form for an atomic symbol of an element X is
[tex]_{Z}^{A}\text{X}[/tex]
where
Z = the atomic number = the number of protons = p
A = the mass number =the number of protons plus neutrons =p + n
So, to get the number of neutrons, you take
A – Z = (p + n) – p = n
In words,
Mass number – atomic number = number of protons
