Question

an atom has 82 protons and a mass number of 208. how many neutrons does it have? 126 208 82 130

Explanation:

Step1: Recall mass - number formula

The mass number ($A$) of an atom is the sum of the number of protons ($p$) and neutrons ($n$), i.e., $A=p + n$.

Step2: Rearrange the formula to find neutrons

We can rewrite the formula as $n=A - p$.

Step3: Substitute given values

Given that $A = 208$ and $p = 82$, then $n=208 - 82$.
$n = 126$

Answer:

A. 126