Private (potassium) Second (Sodium) Class (Calcium) M (Magnesium) a (aluminum) c (Carbon) Z (Zinc) i (iron) t (Tin) l (Lead) He (Hydrogen) Can (Copper) Make (Mercury) Some (Silver) Gun (Gold) Powder (Platinum)
Private Second-class MacZitl he can make some gun powder
I'm pretty sure you get given the reactivity series, along with a periodic table and common ions. You're not expected to know it off by heart anyway, just remember that valuable metals (gold, silver, platinum) is low, copper, helium, hydrogen are low. Then remember some of the higher ones like Potassium, Sodium, Magnesium.