Answer:
K
Explanation:
The reactivity of metals is described by its size. Since metals tend to lose their outer shell electrons in reactions to become positively charged ions, the lower the attraction force between a nucleus and valence electrons, the easier it is to lose those electrons for a metal and become an ion. The greater the size, the lower the Coulombic force between a nucleus and valence electrons
Atomic size increase from right to left across the period and down the group. This implies that potassium has a highest radius and, therefore, is the most reactive.
