Question

protons: 10
neutrons: 10
electrons: 10
what is the mass number?

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 protons and neutrons

Given that the number of protons $p = 10$ and the number of neutrons $n=10$.

Step3: Calculate the mass number

Substitute the values into the formula: $A=10 + 10=20$.

Answer:

20