Question

an atom has 79 protons, 78 electrons, and a mass number of 118. how many neutrons does this atom have? 79 40 78 39

Explanation:

Step1: Recall the formula for mass number

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

Step2: Rearrange the formula to solve for neutrons

We can rearrange the formula to find the number of neutrons: $n=A - p$.

Step3: Substitute the given values

Given that $A = 118$ and $p = 79$, we substitute these values into the formula: $n = 118-79$.

Step4: Calculate the result

$n=39$.

Answer:

39