Answer:
1/2 of the cells.
Explanation:
DNA replication is a semiconservative process which means that one strand of each of the two DNA double helices formed after one round of DNA replication is the parental strand and the other one is the newly formed strand.
Given that a population of the cells was infected with 32P-labeled viruses which would insert its DNA into the host cell's DNA, after one generation of cell division, the 32-P labeled DNA would be present in one strand of all the DNA molecules present in all the cells.
After the second generation of cell division, the 32-P labeled parental strand would be present in 1/2 of the total cells while the rest half of the cells would have only the normal DNA.