Which organism was first used to show semiconservative replication of DNA?

Escherichia coli

The correct answer is Option is (2) - Escherichia coli

The semiconservative mode of DNA replication was initially proposed by Watson and Crick. This hypothesis was later experimentally confirmed by Meselson and Stahl in 1958 through their work on the bacterium E. coli, and Very similar experiments involving use of radioactive thymidine detect distribution of newly synthesised DNA in the chromosomes was performed on Vicia faba (faba beans) by Taylor and colleagues in 1958. The experiments proved that the DNA in chromosomes also replicate semiconservatively.