Question

1) Why should a Magnesium ribbon be cleaned before burning in air ?​

Answer 1

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

Answer:

Magnesium ribbon should be clean before burning to remove the protective layer of zinc oxide