Question

A shiny brown coloured element ‘X’ o n 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?

Answer 1

The shiny brown element is copper.
On heating in air, the following reaction takes place :
Cu + O2 -----> CuO2
The blackish colour shows the deposition of copperoxide on the metal

Answer 2

It's a copper because when copper is placed in the air it become dull in short time .It loses its lustre due to the action of oxygen in the air on it. The action lead to the formation of copper oxide which is dull looking.
Iron and aluminium also behave like that.

hope it will help you.....