The mass number of any atom is always the __ - [4) (1 Poin protons in the nucleus electrons in the nucleus electrons + protons protons+neutrons

## Step 1<br />The mass number of an atom is a measure of the total number of protons and neutrons in its nucleus. This is because protons and neutrons are the particles that contribute to the mass of an atom. Electrons, on the other hand, are much lighter and do not contribute significantly to the mass of an atom.<br /><br />## Step 2<br />The mass number is not the sum of electrons and protons, nor is it the number of protons in the nucleus alone. It is the sum of the number of protons and neutrons in the nucleus.