Question

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

Answer 1

Magnesium is a reactive metal . It reacts with substances present in atmosphere and forms an outer layer above the magnesium ribbon.So it should be cleaned before using.

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.