Answer: S phase (Synthesis).
- A G<sub>1</sub> phase, before DNA synthesis begins
- B S phase (Synthesis)
- C G<sub>2</sub> phase, after DNA synthesis ends
- D Mitosis, during chromosome separation
Correct answer: B. S phase (Synthesis)
Explanation: DNA replication occurs during S phase (Synthesis phase) of interphase, before cell division begins.
The cell cycle: G1 (growth and preparation), S (DNA replication, chromosome number stays 2n but DNA content doubles), G2 (final checks before division), and M (mitosis itself) - together, G1+S+G2 make up interphase.
Concept context
Mitosis and meiosis: how cells divide for growth, repair, and reproduction.