Why should a magnesium ribbon be cleaned before burning

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

Answer:

A magnesium ribbon should be cleaned before burning to remove the layer of magnesium oxide (MgO) that forms on its surface due to reaction with air.

Explanation:

• Magnesium reacts with oxygen in the air to form a thin, white coating of magnesium oxide.

• This oxide layer prevents the magnesium metal underneath from burning properly.

• Cleaning the ribbon (by rubbing it with sandpaper) removes this layer, so that the pure magnesium can burn brightly and react efficiently with oxygen.