one isotope of sodium has 11 protons and 7 neutrons. what is the mass number of this isotope?\n4\n7\n11\n18

Explanation:

Step1: Recall mass - number formula

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

Step2: Substitute given values

We are given that $p = 11$ and $n=7$. Substitute these values into the formula: $A=11 + 7$.

Step3: Calculate the result

$11+7 = 18$.

Answer:

18