The nucleus of an atom contains protons and neutrons only.
To understand why, let’s break it down:
- Protons are positively charged particles found in the nucleus. They define the atomic number of an element, determining what element it is.
- Neutrons are neutral particles that also reside in the nucleus. They contribute to the atomic mass and play a key role in nuclear stability.
- Electrons are negatively charged particles, but they are not found in the nucleus; instead, they orbit around the nucleus in electron shells.
Therefore, the correct answer is (d) protons and neutrons only.