Which method will you expect to kill most vegetative bacteria in the shortest amount of time: boiling in water at 120 degrees celcius or baking in a kitchen oven at 120 degrees celcius? why

Hi bliss 6833!
to my knowledge, it all has to do with heat energy. it takes more heat energy to raise the same volume of water as it does air. inversely, water can release more heat over time since it takes more heat to raise it to that temperature.
this can not only provide more consistent temperature, but we must note that this is assuming you start purging the bacteria once you have reached that temperature.
for more info look up heat of fusion and heat of vaporization. i know autoclaves disinfect at 121 c at 15 psi. since liquids resist compression unlike gases, steam or water can penetrate deeper at the microscopic level.
read this link for more info