# What is the mass number of an atom of potassium that has 18 neutrons?

Jul 7, 2016

Mass Number of Potassium = 37amu.

#### Explanation:

The mass number of an element is determined by adding the number of protons and neutrons in the atom.

Potassium is atomic number 19 on the periodic table.

The atomic number is equal to the number of protons.

Atomic number 19 = 19 protons.
We are told in the question 18 neutrons

Mass number = Protons + Neutrons

Mass number $= 19 + 18$

Mass Number of Potassium = 37amu.