Here's why:

* Electrochemical Series: The reactivity of metals is determined by their position in the electrochemical series. Metals higher on the series are more reactive. Zinc is higher than nickel in the series.

* Standard Reduction Potential: The standard reduction potential (E°) is a measure of the tendency of a metal to gain electrons and be reduced. Zinc has a more negative standard reduction potential than nickel, indicating that it is more likely to lose electrons and become oxidized.

Here are some specific reactions that demonstrate this:

* Reaction with acids: Zinc readily reacts with dilute acids like hydrochloric acid to produce hydrogen gas, while nickel reacts more slowly.

* Corrosion: Zinc is more susceptible to corrosion than nickel.

* Displacement reactions: Zinc can displace nickel from nickel salts in solution.

In summary, zinc is a more reactive metal than nickel due to its higher position in the electrochemical series and its more negative standard reduction potential.