The true statement concerning the atomic nucleus is: it takes up most of the volume of the atom. it contains protons, neutrons, and electrons. it contains most of the mass of the atom. it is made up of electrons only.

It contains most of the mass of the atom.

Explanation:

An atom is smallest unit of a matter or substance.It consist of three subatomic particles : electrons, protons, neutrons.

Protons and neutrons are located in the center of an atom called as nucleus where mass of an atom is concentrated.

Atomic mass = Number of protons + Number of neutrons

Electrons are located outside the nucleus where they orbit in different energy levels around the nucleus.  they have negligible mass as compared to protons and neutrons.

Thus the true statement concerning the atomic nucleus is It contains most of the mass of the atom.