DNA synthesis is takes place in which stage

DNA synthesis takes place in S stage.
In the eukaryotic cell cycle, chromosome duplication occurs during the "S phase" (the phase of DNA synthesis), and chromosome segregation occurs during the "M phase" (the mitosis phase).
The S phase is the period of wholesale DNA synthesis during which the cell replicates its genetic content; a normal diploid somatic cell with a 2N complement of DNA at the beginning of the S phase acquires a 4N complement of DNA at its end.