Why are halogens extremely reactive non metals?
because they require only one electron to form stable configurations of the noble gases
It is true that halogens are most reactive non-metals. This is because of two reasons:- They have only seven electron in their outermost shell. Thus, they get stable configuration only on gaining one electron. Also, halogens are the most electronegative elements and have very attracting power for electrons.
The most reactive goup in the metals is the Alkali metals (Group I) The most reactive non-metal group is Group 17 or VIIA) the Halogens. It is difficult to say which of the two groups is more reactive. Chemists will say that Flourine is the most reactive element. Note that Group 18 is the least reactive, most stable.