Answer: protons and neutrons.
- A protons only
- B protons and electrons
- C protons and neutrons
- D neutrons only
Correct answer: C. protons and neutrons
Explanation: Mass number A = number of protons + number of neutrons (the nucleons).
Bohr's model: electrons occupy fixed circular shells (K, L, M) around the nucleus, with each shell holding up to 2n2 electrons.
Concept context
Explore how electrons are arranged inside an atom. Covers Bohr's model, quantum numbers, Heisenberg's uncertainty principle, shapes of s, p, d orbitals, and electronic configuration rules.