Which subatomic particles are contained in the nucleus of an atom?

The correct answer identifies that the nucleus of an atom contains protons and neutrons. This is fundamental to atomic structure. Protons are positively charged particles, which contribute to the overall charge of the nucleus and play a crucial role in determining the element's identity. Neutrons are neutral particles that provide stability to the nucleus, balancing the repulsive forces between the positively charged protons.

The presence of both protons and neutrons in the nucleus helps to explain not only the behavior of atoms during chemical reactions but also the overall mass of an atom, since these particles comprise most of an atom’s mass. In contrast, electrons are located in the electron cloud surrounding the nucleus and are not found within it, which clarifies why options that mention only electrons or combinations of electrons with protons or neutrons cannot accurately describe the composition of the nucleus.