Answer:
19
Explanation:
The mass of an atom is given by its mass number. This is because the mass of an atom is concentrated at the nucleus.
Mass number = number of protons + number of neutrons
Protons and neutrons are the most massive particles in any atom.
Protons are the positively charged particles in an atom
Neutrons are uncharged particles.
So, the mass number of this atom is:
Mass number = 9 + 10 = 19
