Which statement describes an atomic nucleus?
an atomic nucleus is negatively charged.
an atomic nucleus has no electrical charge.
an atomic nucleus consists of mostly empty space.
an atomic nucleus contains most of the atom’s mass.

An atomic nucleus being negatively charged is incorrect. Electrons allay in the electron cloud. The nucleus is composed of neutrons and protons.

Neutrons: No charge

Protons: Pro-charge or possibly charged.

Electrons: Negatively charged. 

Since a nuclei only composes of no charge and positive charges, overall it would be positive charged. B is also incorrect because the atomic nuclei does give off electrical charges. C is not correct either.

That leaves D, An atomic nucleus contains most of the atom’s mass. This is true because almost all of the atom's mass comes from the protons and neutrons, which again, makes up the nucleus.