Question

what element has a mass number of 15 and 6 neutrons?

Explanation:

Step1: Recall mass - number formula

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

Step2: Calculate the number of protons

We know $A = 15$ and $n=6$. Rearranging the formula $p=A - n$. So, $p=15 - 6=9$.

Step3: Identify the element

The number of protons determines the atomic number of an element. An element with atomic number 9 is fluorine.

Answer:

Fluorine