Question

1. given an elements atomic number and mass number, how can you tell the number of protons and neutrons in its nucleus?

number of protons = mass number, number of neutrons = atomic number - mass number
number of protons = atomic number; number of neutrons = mass number - atomic number
number of protons = atomic number, number of neutrons = mass number + atomic number

Explanation:

Step1: Recall atomic structure concepts

Atomic number ($Z$) is defined as the number of protons in an atom. Mass number ($A$) is the sum of protons ($p$) and neutrons ($n$) in an atom, i.e., $A=p + n$.

Step2: Derive formulas for protons and neutrons

From the definition of atomic number, number of protons $p=Z$. Rearranging the mass - number formula $A=p + n$ for neutrons gives $n=A - Z$.

Answer:

Number of protons = atomic number; number of neutrons = mass number - atomic number.