Answer:
In S or synthesis phase, DNA content of the cell gets doubled. If 2c is the DNA concentration of the cell before S phase then 4c will be the concentration of the DNA after completion of S phase.
However, the chromosome number remains the same.
It is achieved by formation of sister chromatid in the chromosome.
For example, in human cell chromosome number remains the same after S phase, that is, 46.
However, the chromatid number gets doubled, that is, 92.
Thus, the 2n (i.e., 46) number remains the same before and after the S phase.
