The correct option is D Synthesis phase (S)
The phase labelled Y is the synthesis phase (S) of the cell cycle. DNA replication takes place during this phase. If the initial quantity of DNA in the cell is denoted as 2N, then after replication, it becomes 4N. However, the number of chromosomes does not vary. If the number of chromosomes during the G1 phase was 2n, it will remain 2n at the end of the S phase. The centriole in the cytoplasm also divides into the cells that contain centrioles.