Lederberg replica plate exp. on E.coil bacteria was performed to identify the most fittest. lederberg ne master plate pe dekha jab unhone antibiotic (penecilin) ko introduce kiya toh kewal wahi bacteria survive kia jinke pass antibiotic resistance gene present tha.. so it's an example of natural selection.

The correct answer is option 'C': Lederberg and Lederberg.

**Explanation:**
- The replica plate experiment was performed by Joshua Lederberg and Esther Lederberg in 1952.
- The experiment was designed to study the genetic recombination and mutation rates in bacteria, specifically Escherichia coli (E.coli).
- The Lederbergs used this experiment to demonstrate the phenomenon of bacterial conjugation, which is the transfer of genetic material between bacterial cells.
- The experiment involved creating replica plates, which are exact copies of the original plate containing bacterial colonies.
- The Lederbergs used a technique called replica plating to transfer bacterial colonies from the original plate to multiple replica plates.
- The replica plates were made by pressing a sterile velvet cloth onto the original plate, picking up bacterial colonies, and then transferring them onto fresh agar plates.
- By comparing the colonies grown on the replica plates to the original plate, the Lederbergs were able to identify genetic changes that had occurred in the bacteria.
- The experiment allowed the Lederbergs to study the frequency of mutation and recombination events in the bacteria population.
- Through this experiment, they discovered that bacteria could exchange genetic material through conjugation, which has important implications for the spread of antibiotic resistance.
- The replica plate experiment provided a valuable tool for studying bacterial genetics and has been widely used in microbiology research since its development by the Lederbergs.

In conclusion, the replica plate experiment on E.coli bacteria was performed by Joshua Lederberg and Esther Lederberg. This experiment allowed them to study genetic recombination and mutation rates in bacteria and led to the discovery of bacterial conjugation.