How does the idea of a neutron help address the puzzles about the protons in the nucleus and the
mass of atoms?

The sum of the number of neutrons and protons gives the mass number.

Explanation:

n other words, when the number of neutrons is known and the atomic number of an element is known, it becomes easier to determine the approximate mass number by adding the two. Therefore, when the number of neutrons and protons are known, mass number is made the subject of the formula and get its value.

Generally,

Mass number = Number of protons + Number of neutrons.

Number of protons= Mass number - Number of neutrons

Number of neutrons = Mass number - Number of protons.