The correct answer is Choice B, atom. An atom is the smallest unit of matter that contains protons, neutrons, and electrons. To determine the answer, you can recall some basic knowledge about the structure of matter. Atoms are composed of protons, neutrons, and electrons. Protons have a positive charge, neutrons have no charge, and electrons have a negative charge. They are the building blocks of all matter and make up everything we see around us. Organelles, cells, and organisms are all larger structures that are made up of multiple atoms.
