Question

why should a magnesium ribbon be cleaned before burning it in air​

Answer 1

magnesium ribbon should be cleaned before burning in air to remove the layer of magnesium oxide

Answer 2

hey friend!
YOUR answer 》

Magnesium ribbon must be cleaned before burning in air so that the layer of magnesium oxide ( which is formed due to reaction of magnesium with air ) can be removed in order to get the desired chemical reaction.

HOPE it helps you.