International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

What particles are located in the nucleus of an atom?

1. Electrons and neutrons

2. Protons and electrons

3. Protons and neutrons

4. Neutrons and positrons

The correct answer is: Protons and neutrons

The nucleus of an atom consists of protons and neutrons. Protons are positively charged particles, while neutrons carry no charge (they are neutral). Together, these particles account for the majority of an atom's mass and are essential in defining the atomic identity; for instance, the number of protons determines the element's atomic number. Electrons, which are negatively charged, are not found in the nucleus; instead, they orbit the nucleus at various energy levels in what is often referred to as an electron cloud. Options involving electrons—except in the context of their location outside the nucleus—do not accurately describe what is contained within the nucleus. The option involving positrons is also not applicable since positrons are the antiparticles of electrons and do not form part of a typical atomic nucleus. Thus, the correct pairing of protons and neutrons as the primary constituents of the nucleus emphasizes their central roles in atomic structure and stability.