How many identical double strands of DNA will be present after three rounds of replication?

four

six

eight

nine

Every time you replicate DNA you get 2 new DNA and 1 strand of each DNA is composed of the parent strand. So after 3 rounds of replication ...

1 - - > 2 - - - > 4 - - - > 8

Out of these 8, 2 of them contain the parent strands. So 2/8 = 1/4 = 25%

Thus the answer is the third option, eight (8).