Which is made up of protons, neutrons, and electrons, and has its protons and neutrons in the center (nucleus)?

• A. Atom
• B. Molecule
• C. Dust speck
• D. Cell

Answer: (A)

Atomic structure is being tested here. An atom is composed of a central nucleus that contains protons and neutrons, with electrons circling around in an electron cloud. The nucleus holds the positively charged protons and the neutral neutrons at the center, giving the atom most of its mass, while the electrons occupy space around it. A molecule is simply two or more atoms bonded together, not a single atom with its own nucleus. A dust speck isn’t a defined unit of matter in this context, and a cell is a larger biological unit that can include a nucleus but represents a different level of organization. So the description matches an atom.