The correct order of reactivity of the elements is given by option 4: Na > Mg > Zn > Cu.

Reactivity is a measure of how easily an element undergoes a chemical reaction. In general, metals tend to lose electrons and form positive ions, which makes them more reactive.

Sodium (Na) is the most reactive metal among the given options. It readily loses one electron to form a stable positive ion.

Magnesium (Mg) is less reactive than sodium but more reactive than zinc and copper. It also loses two electrons to form a stable positive ion.

Zinc (Zn) is less reactive than both sodium and magnesium. It loses two electrons to form a stable positive ion.

Copper (Cu) is the least reactive among these elements. It only loses one electron to form a positive ion.

Therefore, the correct order of reactivity from most reactive to least reactive is Na > Mg > Zn > Cu.