Question

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

Answer 1

Answer:

in order to remove the oxide layer from the ribbon...

Answer 2

$\huge\mathcal{\fcolorbox{cyan}{black}{\pink{Answer}}}$

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.

Explanation:

Hope it helps you...