Which of the following best describes the structure of an atom?

• A. An atom is made up of only protons and neutrons, with no electrons.
• B. An atom consists of a dense nucleus containing protons and neutrons, surrounded by electrons in defined energy levels.
• C. An atom consists of a nucleus made of electrons, with protons and neutrons orbiting around it.
• D. An atom is a solid sphere composed entirely of electrons.

Answer: (B)

Verified step by step guidance

1. Recall the basic structure of an atom: it consists of a central nucleus and electrons surrounding it.
2. Understand that the nucleus contains protons, which are positively charged, and neutrons, which have no charge.
3. Recognize that electrons are negatively charged particles that occupy specific energy levels or orbitals around the nucleus.
4. Note that the nucleus is very dense and contains almost all the atom's mass, while electrons occupy most of the atom's volume but contribute very little mass.
5. Conclude that the correct description is: an atom consists of a dense nucleus containing protons and neutrons, surrounded by electrons in defined energy levels.