Out of the options, "Iron" is the most dense here.
In short, Your Answer would be Option D
Hope this helps!
It's genre. Look for something either on a final or starting page near the cover, and check to look if it's non fiction, or anything else that could prove it as reliable.
Nice written.
Is it written by you yourself or you have copied it from somewhere?
Generally speaking the larger, more massive elements are less stable, like isotopes of elements. With this said, they are less likely to react since they will become heavy and unstable. This is why chlorine is more reactive with other elements like sodium than astatine.
