The shiny brown coloured element X that turns black on heating in air is most likely copper (Cu).



When copper is heated in air, it reacts with oxygen to form copper oxide (CuO), which is black in colour. The chemical reaction that takes place can be represented by the following equation:

2Cu + O2 → 2CuO

The black compound formed is copper oxide (CuO). It is an inorganic compound that is used in the production of various materials, such as ceramics, glass, and pigments.



The reason why copper turns black on heating in air is due to the reaction between copper and oxygen. When heated, the atoms in the copper gain energy and start to vibrate more rapidly. This increased kinetic energy allows the copper atoms to react with the oxygen molecules in the air.

The copper oxide that is formed is black in colour because it absorbs all the visible wavelengths of light and reflects very little. This gives it the appearance of being black.

In conclusion, the shiny brown coloured element X that turns black on heating in air is most likely copper (Cu). When heated, it reacts with oxygen to form copper oxide (CuO), which is black in colour. This is due to the absorption of all the visible wavelengths of light by the compound.

Element X is copper which is shiny brown metal whereas the black colour compound is Copper Oxide which is formed when copper reacts with air on heating.