Zinc is more reactive than iron, Magnesium is more reactive than both.
Reactivity series, here is how you learn it:
K Kitten
Na not
Ca Cat
Mg make
Al a
Zn Zoo
Fe For
Pb Poor
H2 Hungry
Cu Childeren
Ag (and these too just learn them silver comes first and then gold)
Au
So the sentence is: kitten not cat, make a zoo for poor hungry children, silver and then gold.
Learn the reactivity series, it will help you.