Question

what is the mass number of an atom that has 12 protons, 13 neutrons, and 13 electrons?
13
26
12
25

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: Identify values of $p$ and $n$

Given that $p = 12$ and $n=13$.

Step3: Calculate the mass number

$A=12 + 13=25$.

Answer:

D. 25