The correct answer is C. Paul Muller.
Paul Hermann Müller (1899-1965) was a Swiss chemist who discovered the insecticidal properties of DDT in 1939. He was awarded the Nobel Prize in Physiology or Medicine in 1948 for his discovery.
Othmanzedicer was a Turkish physician who first synthesized DDT in 1874. However, he did not recognize its insecticidal properties.
R.H. Painter was an American chemist who independently discovered the insecticidal properties of DDT in 1939. However, he did not publish his findings until after Müller had published his.
Rachel Carson was an American marine biologist and conservationist who wrote the book Silent Spring, which is credited with launching the environmental movement. She did not discover the insecticidal properties of DDT.