A neutral atom of sodium (Na) has an atomic number of 11 and a mass number of 23. How many neutrons would be found in the nucleus of this atom of sodium?

A neutral atom is an atom that has no charge, which means it has no additional electrons or electrons removed from its energy levels.
An atom is made up of sub-atomic particles neutrons and protons found in the nucleus and electrons found in the energy levels.
The number of protons in the nucleus of a neutral atom is known as the atomic number.
In a neutral atom, the atomic number is equal to the number of electrons as protons are equal to the number of electrons.
The sum of protons and neutrons in the nucleus of an atom is known as the mass number of an atom.

Therefore;

Protons = Atomic number

Protons + neutrons = Mass number

Thus;

Neutrons = Mass number - protons or

= Mass number - atomic number

In this case;

Atomic number = 11

Mass number = 23

Thus;

Neutrons = mass number - atomic number

= 23 - 11

= 12 neutrons