(a) at the bottom of the reactivity series
(b) at the top of the reactivity series.
(c) just below copper in the reactivity series
(a) At the bottom of the reactivity series the metal which has been placed is Gold.
(b) At the top of the reactivity series the metal which has been placed is Potassium.
(c) Just below copper in the reactivity series the metal which has been placed is Mercury.