Ans.
During DNA replication, a single parent DNA molecule provides two daughter DNA molecules, each having one old and one new DNA strand in one round of replication.
After first round of replication, two copies of DNA molecules are formed from a single DNA molecule. Now, these two copies will act as parent DNA molecules, and after second round of replication, four copies of DNA molecules are formed.
Thus, the correct answer is 'option). 4.'