At which phase of cell cycle DNA replication takes place ?

S phase .

The correct answer is Option (2) - S phase

In eukaryotes, DNA replication takes place during the S (synthesis) phase of the cell cycle. During this phase, the cell duplicates its entire genome in preparation for cell division.

Other options:

G2 phase (incorrect): because G2 phase is the phase of the cell cycle that follows DNA synthesis and precedes cell division (M phase).

M phase (incorrect): because during this phase, the cell undergoes mitosis, the process of separating replicated chromosomes into two daughter cells.

G1 phase (incorrect) because G1 phase is the first phase of the cell cycle and occurs before DNA synthesis. During this phase, the cell grows and prepares to enter the S phase.