Answer: 12C and 14C.
- A 12C and 14C
- B Na and Mg
- C O<sub>2</sub> and O<sub>3</sub>
- D H<sub>2</sub>O and CO<sub>2</sub>
Correct answer: A. 12C and 14C
Explanation: Carbon-12 and carbon-14 are isotopes because both are carbon atoms but have different mass numbers.
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.