Question

why should magnesium ribbon be cleaned before burning in air ?​

Answer 1

Heya...

When the Mg ribbon is kept untouched, the Mg ribon reacts with the surrounding air (oxygen) and forms Mg oxide. Therefore te Mg ribbon should be cleaned before burning in air to get the desired chemical reaction.

Hope it helps... :)

Answer 2

Magnesium ribbon should be cleaned before burning in air because in air it react with oxygen and form a layer of magnesium oxide on the surface.