Question

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

Answer 1

Explanation:

Magnesium ribbon should be cleaned with sandpaper before burning in the air. ... To remove the Magnesium oxide layer from the ribbon which may prevent or slow down the burning of magnesium ribbon. Unwanted impurities deposited on the magnesium ribbon can be removed and only pure magnesium can be used for the reaction.

Answer 2

Because the layer of magnesium oxide (which is formed due to the reaction of magnesium with air) can be removed in order to get the desired chemical reaction.