Question

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

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 values

Given that $p = 10$ and $n=10$, we substitute these values into the formula: $A=10 + 10$.

Step3: Calculate result

$A = 20$.

Answer:

20