Question

why should a magnesium ribbon be cleaned before burning in air

Answer 1

Because a layer of magnesium oxide on the magnesium rebbion.

Answer 2

we must clean the magnesium ribbon before burning in air because to remove the oxide layer of magnesium or magnesium oxide layer ......if we will not clean the ribbon then it will not burn in air . so to burn it in air it is necessary to remove the magnesium oxide layer

hope! this will help you.....