Atomic Nucleus Composition

Steps:

• Recall that atoms consist of a central nucleus surrounded by electrons.
• Identify the nucleus as the dense core holding most of the atom's mass.
• Remember protons carry positive charge and define the element.
• Note neutrons are neutral particles that stabilize the nucleus.

Why D is correct:

• By atomic structure definition, the nucleus contains protons (positive charge) and neutrons (no charge) to form the atom's core.

Why the others are wrong:

• A: Electrons orbit outside the nucleus, not inside.
• B: Protons are also present; neutrons alone cannot define an element.
• C: Electrons reside in electron cloud, not the nucleus.

Final answer: D