Answer: Option (3) is the correct answer.
Explanation:
An atom consists of three sub atomic particles which are protons, neutrons, and electrons.
Protons have a positive charge, neutrons have no charge, and electrons have a negative charge.
Both protons and neutrons are placed inside the nucleus of an atom. This nucleus is surrounded by the electrons as electrons revolve around the nucleus.
Thus, we can conclude that out of the given options, a core of protons and neutrons surrounded by electrons best describes an atom.