Question

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

Answer 1

Answer:

Explanation:

Mg is highly reactive and when it is kept in the open it can react with air, cleaning the ribbon will remove the impurities formed due to the reaction with air, so then you will obtain the Mg you need. This is why it is cleaned before usage.

Answer 2

Answer:

because magnesium is a highly reactive element , react with oxygen and moisture present in atmosphere which make a layer of oxide . This layer of oxide is quite stable and prevent magnesium from further reaction