Which of the following ions if reduced under standard conditions will have negative reduction potential?

${\mathrm{Zn}}^{2+}$ is less readily reduced than ${\mathrm{H}}^{+}$ whereas ${\mathrm{Cu}}^{2+},{\mathrm{Au}}^{3+}$ and ${\mathrm{Hg}}_2^{2+}$ are more readily reduced. Thus, ${\mathrm{Zn}}^{2+}\mid \mathrm{Zn}$ has negative reduction potential.

The term "reduction potential" (Eo) refers to a chemical species' propensity to undergo reduction by obtaining an electron. It is used in electrochemistry to characterize hydrogen, which typically has a reduction potential of zero [24].