While Abhi was about to burn magnesium ribbon in the chemistry laboratory, the teacher asked him to clean the ribbon with the sand paper before burning it.
What could be the reason for the above instruction by the teacher? After burning the magnesium ribbon, Abhi obtained a white coloured residue. Name this residue. What type of chemical reaction has occurred? Write a balanced chemical equation to explain the reaction.

Explanation

Magnesium reacts with atmospheric oxygen to develop a layer of magnesium oxide. This layer does not allow the underlying magnesium to undergo combustion.
Magnesium oxide, Combination reaction.
`2Mg + O_2 to 2MgO`