A shiny brown coloured element 'X' on heating in air becomes black in colour. Can you predict the element 'X' and the black coloured substance formed? How do you support your predictions?

Explanation

The brown coloured element is copper (Cu). On heating copper reacts with oxygen present in the atmosphere to form copper oxide which is black in colour.
The reaction is shown below.
`Cu_((s))+O_(2(g))overset("Heat")rarr 2CuO_((s))`
If we pass hydrogen gas over hot copper oxide we will notice that black coating on copper turns brown because copper oxide loses oxygen to form copper.
`CuO_((s))+H_(2(g))overset("Heat")rarr Cu_((s))+H_(2)O_((s))`
This will support our prediction.