Where are protons and neutrons located within an atom?

Protons and neutrons are located in the nucleus of an atom, which is at the center and serves as the core of the atom. The nucleus contains nearly all of the atom’s mass because protons and neutrons are substantially heavier than electrons.

Understanding the role of the nucleus is fundamental in chemistry as it defines the identity of the element (through the number of protons) and contributes to atomic mass (the combined number of protons and neutrons).

This contrasts with the other locations mentioned in the options. The outer shell refers to the electron configuration of an atom, which involves the arrangement of electrons around the nucleus and does not participate in the mass of the atom. The electron cloud describes the region surrounding the nucleus where electrons are likely to be found, and energy levels refer to the specific regions where electrons reside but do not include protons or neutrons. Hence, the correct answer emphasizes the central role of the nucleus in the atomic structure.