In isolation of which one of the following metals from their ores,...

For $ZnS, KCN$ is used as depressant.

In the metallurgy of silver and gold, the respective metal is leached with a dilute solution of $NaCN$ or $KCN$ in the presence of air, which supplies ${O}_{2}$. The metal is obtained later by replacement reaction.

$4M\left(s\right) + 8{CN}^{-}\left(aq\right) + 2{H}_{2}O\left(aq\right) + {O}_{2}\left(g\right) \to 4{\left[M{\left(CN\right)}_{2}\right]}^{-}\left(aq\right) + 4{OH}^{-}\left(aq\right)\left[M = AgorAu\right]$

$2{\left[M{\left(CN\right)}_{2}\right]}^{-}\left(aq\right) + Zn\left(s\right) \to {\left[Zn{\left(CN\right)}_{4}\right]}^{2 -}\left(aq\right) + 2M\left(s\right)$

Copper metal is not involved in this process.