protons: 5\nneutrons: 5\nelectrons: 5\nwhat is the mass number? 0

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: Identify values of protons and neutrons

Given that $p = 5$ and $n=5$.

Step3: Calculate the mass number

Substitute the values into the formula: $A=5 + 5=10$.

Answer:

10