Question

what is the mass number of nitrogen if it has 8 neutrons *
your answer

carbon has three isotopes: *
n - 12
n - 13
n - 14

Explanation:

Step1: Recall nitrogen's atomic number

Nitrogen's atomic number ($Z$) is 7, which means it has 7 protons.

Step2: Use mass - number formula

The mass number ($A$) is the sum of protons and neutrons. Given neutrons ($n$) = 8 and protons ($p$)=7. So $A=p + n$.
$A=7 + 8$

Answer:

15