Carbon, if not wiki it
Chlorine (halogen), because Argon is a Nobel gas
No element in period 3 has an atomic mass of 12.
Bromine. :)
Ar(argon)
Fluorine.
In the fourth period of the periodic table of elements, the most reactive element is potassium. It is an alkali metal, and it has the atomic number of 19.
The first element in a period is an alkali metal.
The most chemically active non-metal, and the most reactive element overall, is fluorine. Fluorine has an extremely high electronegativity, meaning that it will remove an electron form almost anything. Therefore, it is amazingly reactive, and it even reacts with glass.
it is a nonmetal.
it is a nonmetal.
Sodium has the largest atomic size in the third period.
it is a nonmetal.