After one round of DNA replication, of the DNA will contain only 14N, of the DNA will contain only 15N, and of the DNA will be of an intermediate density.

After one round of DNA replication, none of the DNA will contain only 14N, none of the DNA will contain only 15N, and all of the DNA will be of an intermediate density.

Explanation:

In order to rule out the conservative model of DNA replication and discover that it in fact a semi-conservative model, this technique was employed to check for what ratio of N15 and N14 was present in cells that had undergone the process of replication. The former would've resulted in equal densities of both N14 and N15.

oxygen +1 most likely

c. live where it’s cold and icy