Which lists these metals in order from most reactive to least reactive? calcium, magnesium, strontium

Stronium, calcium and then magnesium.

All three of them are elements from group 2 of the periodic table and their reactivity increases down the group. As the size of atoms increases, ionization energy decreases, shielding from inner electrons increase and it becomes easier for the elements to lose their valence electrons. Thus magnesium is the smallest in size, then calcium and then stronium. Stronium with the largest size is most reactive.