Final answer:
Group 1 elements, also known as alkali metals, are the most reactive metals due to having 1 valence electron.
Step-by-step explanation:
The Group 1 elements are the most reactive metals because they have 1 valence electron. The valence electron is located in the outermost shell of an atom and is involved in chemical reactions. Since the Group 1 elements have only one valence electron, it is easier for them to lose this electron and form a positive ion, leading to their high reactivity.