The metal that violently react in dilute acid?

You do have a printed periodic table, right? You can get the information at http://www.chemicalelements.com/index.html but you really need your own printed copy to carry with you. It will be a primary reference for everything you do.

Potassium is in group one, which means it has one electron in the outer shell, which means it is very reactive because that one electron is easily lost. Potassium is so reactive that it will strip oxygen away from water and generate enough heat to ignite the hydrogen as it is released. The part about dilute acid was only a distraction.