Question

before burning in air The magnesium ribbon is cleaned by rubbing with a sand paper to:​

Answer 1

Like rusting in case of iron, with magnesium, the oxide layer forms a white coating on the outside of the metal that will slow down or interfere with the burning process. Rubbing with sand paper helps to remove this oxide layer due to which burning speeds up.

Answer 2

Rubbing with sand paper helps to remove the oxide layer which form as a coating outside the magnesium bar .