Relative to the sum of the masses of its constituent nucleons, the mass of a nucleus is: greater the same smaller sometimes greater and sometimes smaller

Answer is: smaller.

Protons and neutrons are in the nucleus of an atom.

Nuclear energy is the energy found in the nucleus of an atom.

The missing mass of a nucleus is called its  binding energy, the energy needed to break it up  into separate protons and neutrons.

Average binding energy per nucleon equals total  binding energy divided by mass number (sum of protons and neutrons in an atom).

it's c. elements are placed in rows based on how may valencies electrons have.