Answer:
#See solution for details.
Step-by-step explanation:
-The process of converting one chemical into another is called Nuclear Transmutation.
-A transmutation can be achieved either by nuclear reactions (in which an outside particle reacts with a nucleus) or by radioactive decay (where no outside particle is needed).
-This process was not yet developed 1000years ago thus the inability to convert lead into gold back then.
-The process didn't exist and wasn't applied in modern physics until 1901 by Frederick Soddy together with Ernest Rutherford discovered the radioactive Thorium.