**Core Concept**
The process being tested involves the semi-conservative replication of DNA, a fundamental concept in molecular biology. Semi-conservative replication is the process by which DNA replicates, resulting in one old strand and one new strand in each daughter molecule.

**Why the Correct Answer is Right**
During semi-conservative replication, the leading strand is synthesized continuously, while the lagging strand is synthesized in short, discontinuous segments known as Okazaki fragments. When DNA replicates twice, the original radioactive DNA strands are diluted, but not completely removed. After two rounds of replication, the resulting DNA molecules will have a mix of radioactive and non-radioactive strands, but the original radioactive strands will still be present in each molecule.

**Why Each Wrong Option is Incorrect**
**Option A:** This option suggests that all radioactive DNA is completely removed after two rounds of replication. However, semi-conservative replication ensures that some original radioactive strands are retained in each daughter molecule.

**Option B:** This option implies that the radioactive DNA is completely diluted and replaced with non-radioactive DNA after two rounds of replication. However, the original radioactive strands are still present in each molecule.

**Option C:** This option suggests that the radioactive DNA is concentrated in one of the daughter molecules. However, semi-conservative replication results in a mix of radioactive and non-radioactive strands in each molecule.

**Option D:** This option is incorrect because it implies that the radioactive DNA is completely removed from the system after two rounds of replication.

**Clinical Pearl / High-Yield Fact**
Semi-conservative replication is a fundamental concept in molecular biology, and understanding this process is crucial for understanding the mechanisms of DNA replication, repair, and recombination.

**Correct Answer: B. The resulting DNA molecules will have a mix of radioactive and non-radioactive strands.**