Final answer:
Howard Florey and Ernst Chain are credited with isolating Penicillin G. They purified and mass-produced it at Oxford University, leading to them, along with Alexander Fleming, being awarded the Nobel Prize in Physiology and Medicine in 1945.
Step-by-step explanation:
The individuals credited with isolating Penicillin G are Howard Florey and Ernst Chain, who worked at Oxford University. Although Alexander Fleming discovered penicillin in 1928, it was Florey and Chain who, in 1940, purified penicillin and confirmed its effectiveness as an antimicrobial agent, leading to the mass production necessary for medical use. As a result of their significant contributions, Fleming, Florey, and Chain were jointly awarded the Nobel Prize in Physiology and Medicine in 1945 for their groundbreaking work in the discovery and development of penicillin.