When iron and sulphur are heated at high temperature, black colored FeS is formed.

Explanation:
When iron (Fe) and sulphur (S) are heated together at high temperature, a chemical reaction takes place between them, resulting in the formation of iron sulphide (FeS). This reaction is known as a synthesis reaction.

The reaction can be represented by the following equation:
Fe + S → FeS

Here's a detailed explanation of the reaction:

1. Formation of iron sulphide (FeS):
When iron and sulphur are heated together, their atoms gain energy and become more reactive. The iron atoms react with the sulphur atoms to form iron sulphide. The iron atoms lose electrons and form positive ions, while the sulphur atoms gain electrons and form negative ions. These oppositely charged ions attract each other and form a compound called iron sulphide (FeS).

2. Color change:
The formation of iron sulphide results in a change in color. Iron sulphide is black in color, which gives the reaction mixture a black appearance.

3. Chemical properties of iron sulphide:
Iron sulphide is a compound that has different properties from its constituent elements, iron and sulphur. It is a solid with a crystalline structure. Iron sulphide is insoluble in water and has a higher melting point compared to iron and sulphur individually.

4. Possible uses of iron sulphide:
Iron sulphide has various applications in different industries. It can be used as a pigment in black inks, paints, and dyes. It is also used in the production of fireworks and as a catalyst in certain chemical reactions.

In conclusion, when iron and sulphur are heated at high temperature, a chemical reaction takes place, resulting in the formation of black colored iron sulphide (FeS). This reaction is a synthesis reaction, where iron and sulphur combine to form a new compound with different properties.