Question

what is the mass number?

Explanation:

Step1: Identify protons and neutrons

Count the number of protons and neutrons in the nucleus. Protons are red - colored and neutrons are black - colored in the nucleus. There are 2 protons and 2 neutrons.

Step2: Calculate mass number

The mass number (A) is the sum of the number of protons (p) and neutrons (n). So, $A=p + n$. Substituting $p = 2$ and $n=2$, we get $A=2 + 2$.
$A = 4$

Answer:

4