The most nonactive elements are the noble gases (helium, neon, krypton, xenon, and radon). Platinum is also quite inactive, almost as inert as a noble gas.
The most abundant element in the universe is Hydrogen (H). The second most common is Helium (He). However, these are only found in trace amounts on Earth.
Plutonium is considered a very toxic element; it accumulates in the body without being easily metabolized or eliminated, doses as low as 5,000 total particles can be enough to increase the risk of...