A shiny brown coin made up of an element turned black on heating. What was the element of the coin and what is the black compound formed?
From the description, it can be concluded that the element of the coin is copper.
On being heated copper gets oxidized due to the presence of oxygen in air which results in the formation of copper oxide (precisely cupric oxide) which is black in color.
The reaction is as follows:
2Cu + O2→ 2CuO