Question

WHY SHOULD A MAGNESIUM RIBBON BE CLEANED BEFORE BURNING IN AIR

Answer 1

Because magnesium ribbon has a small layer of MgO in them .... thus it has to be cleaned before burning in air

Answer 2

Magnesium is a highly reactive element. It forms magnesium oxide when it combines with oxygen. This Magnesium oxide is stable and it prevents further reaction with oxygen. Therefore to remove this coating it is cleaned with sand paper.