Sodium, aluminum, and magnesium are metals. For metals, reactivity decreases as you go from left to right across the periodic table. The least reactive of those three is therefore aluminum.
It is Rust.
Zinc was found by mistake. It's the German word for zink. And it was found in Greece.
Andreas Sigismund Marggraf rediscovered Zinc in India in 1746.
In the mineral called Cuprite
since KOH is an base... it should turn de litmus ppr blue...