Explanation:

An atom has a mass number of 37 contains 20 neutrons (17 protons + 20 neutrons = 37 particles in the nucleus).Together, the number of protons and the number of neutrons determine an element's mass number. Since an element's isotopes have slightly different mass numbers, the atomic mass is calculated by obtaining the mean of the mass numbers for its isotopes.bA proton is a subatomic particle, symbol p or p? , with a positive electric charge of +1e elementary charge and a mass slightly less than that of a neutron. Protons and neutrons, each with masses of approximately one atomic mass unit, are collectively referred to as "nucleons".