What is the family of elements that contains the most reactive metals?
The family that contains the most reactive metals are the alkali metals.
Alkali metals are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).
As you move down the column, the metals become more reactive because the nucleus gains more electrons and protons (more electron levels), weakening their electrostatic force. Imagine that you're holding a bunch of books. You can't hold them all very easily, right? It's easy to drop one, which is why it's easy for them to donate 1 electron at STP.
This is why they're so dangerous because they can react easily with any element that doesn't have a full octet (complete set of valence electrons). For example, you wouldn't want any these reacting with fluorine because it has 7 electrons and really wants one more; it's got the highest electrostatic force because of its high nuclear charge and lesser amt. of electron shells. So, the alkali really wants to give one, and the halogens really want one, which is why they're so dangerous.