Radiation Safety Practice Exam

Which of these is a characteristic of an atom?

1. Varied electron layers

2. A single central nucleus

3. Unstable isotopes

4. Variable neutron count

The correct answer is: A single central nucleus

A characteristic of an atom is that it has a single central nucleus. This nucleus contains protons and neutrons and serves as the dense core around which the atom's electrons orbit. The presence of a central nucleus is fundamental to what defines an atom, as it holds the majority of the atom's mass and contains positively charged protons that contribute to the chemical identity of the element. The structure of the atom is thus primarily organized around this nucleus, with electron layers or shells existing in the space surrounding it. While the nucleus can have variable neutron counts, leading to different isotopes, the atom always maintains a central nucleus regardless of its specific variations in mass or stability.