Answer : The reactivity order from most reactive to least reactive will be:
Potassium > Calcium > Chromium
Step-by-step explanation:
Chemical reactivity : It is defined as the tendency of an element to loose or gain electrons.
Metals are the elements which loose electrons and hence, their chemical reactivity will be the tendency to loose electrons.
Their chemical reactivity decreases as we move from left to right in a period because the valence shell come closer to nucleus as we move from left to right. So, tendency to loose electrons becomes difficult due to greater attraction between nucleus and valence electron.
Thus, the reactivity order from most reactive to least reactive will be:
Potassium > Calcium > Chromium