Hershey and Chase used ${}^{35}\mathrm{S} \mathrm{and} {}^{32}\mathrm{P}$, to prove that DNA is the genetic material. Their experiments proved that DNA is genetic material because

In Hershey and Chase experiment  bacteria which was infected with viruses that had radioactive DNA were radioactive, indicating that DNA was the material that passed from the virus to the bacteria. Bacteria that were infected with viruses that had radioactive proteins were not radioactive. This indicates that proteins did not enter the bacteria from the viruses. DNA is therefore the genetic material that is passed from virus to bacteria .