Answer:
The reactivity greatens the farther you go down on the periodic table. Lithium will have the weakest reaction, and cesium will have the greatest reaction. Patterns like this are useful to scientists because it shows which elements are the most reactive and which aren't. The farther down and to the left you go within the periodic table, the more reactive the elements become. The farther up and to the right you go, the less reactive they become.
Explanation:
The answer is calcaneus (heel bone) :)
