Well, for starters, if it explodes and you become harmed, injured, mamed, disfigured, dead or disintegrated, then you have your answer, just have your pen and notebook ready when you test any element that you think may be reactive, because you JUST MAY not have much time to write that sucker down.
If the element has a full valence shell, such as the noble gases, then it is unreactive. It the element is missing few valence electrons of has few valence electrons, then the element is very reactive, such as the sodium.
Lithium is more reactive.
The heaviest element that is highly radioactive is Ununoctium, which has an atomic number of 118.
I would easily say that Fluorine is the most reactive element in the world. Fluorine is the most electronegative of all elements and will react with all elements. It is so reactive that it cannot be found alone in nature.
It is not true; many metals are very reactive and several nonmetals are nonreactive.
Halogens.
bromine!
Nitrogen is a group 5A element that is highly reactive and essential for plant growth.
Gold is highly malleable and almost non-reactive.
rubidium
Chlorine is a Highly reactive element.
Plutonium is not highly reactive under normal conditions. It is a relatively stable element that does not react readily with air or water. However, it can be reactive in certain chemical reactions or when exposed to high-energy particles.
Bromine.
A reactive non metal is an element that can gain the electrons or is more electronegative
Pure sodium is a highly reactive element. When placed in water, sodium will actually explode, producing flames and concussive forces.
Chlorine and fluorine, with fluorine more reactive. Some would also include oxygen. (The two remaining halogens are not gaseous at room temperature.)
Cerium is reactive but not highly reactive.