Which of the following will reduce copper?
zinc
mercury
fluorine
chlorine

The correct answer is Zinc.

Explanation:

Reactivity is defined as the tendency of an element to loose or gain electrons. Metals which loose electrons easily will be considered as more reactive metal.

The reactivity of elements will be judged on the basis of reactivity series. The elements which lie above in the series are more reactive than the elements which lie below in the series. The metals which lie above in the series will easily reduce the metals which lie below in the series.

Copper is the metal which lie above mercury and below zinc.

Thus, zinc is more reactive metal than copper and hence will easily reduce copper from its reaction.

Hence, the correct answer is Zinc.