Final answer:
The element being described is a gas that is unreactive and can weaken Superman in the comic book world.
Step-by-step explanation:
The subject of this question is Chemistry and the grade level is High School.
The element being described in the question is a gas that is unreactive. One example of an unreactive gas is sulfur hexafluoride. This gas is often used as a spark suppressant in electrical devices.
In the comic book world, a mineral containing this unreactive gas could weaken Superman. This suggests that the gas has properties that can neutralize or dampen Superman's powers, making him vulnerable.