It should be cleaned because to remove the protective layer of magnesium oxide..

Introduction:
Before burning a magnesium ribbon in air, it is important to clean the ribbon thoroughly. Cleaning the magnesium ribbon helps to ensure a more efficient and controlled combustion process. This process involves removing any impurities or oxide layers that may be present on the surface of the ribbon.

Reasons for cleaning the magnesium ribbon before burning:

1. Removal of impurities:
Magnesium ribbons are often coated with impurities such as dirt, grease, or other substances due to their handling and storage. These impurities can interfere with the combustion process and affect the accuracy of the experiment. By cleaning the ribbon, these impurities can be removed, providing a clean surface for combustion.

2. Removal of oxide layer:
Magnesium reacts with oxygen in the air to form magnesium oxide (MgO) on its surface. This oxide layer can act as a barrier, preventing the magnesium from reacting further with oxygen during combustion. By cleaning the ribbon, this oxide layer can be removed, allowing for a more complete reaction between magnesium and oxygen.

3. Enhanced combustion:
Cleaning the magnesium ribbon ensures that it is free from any substances that could inhibit the combustion process. A clean surface allows for better contact between the magnesium and oxygen in the air, promoting a more efficient and vigorous combustion reaction. This leads to a brighter and more visible flame, making it easier to observe and analyze the combustion process.

Methods of cleaning magnesium ribbon:

1. Mechanical cleaning:
Mechanical cleaning involves physically removing any impurities or oxide layers from the surface of the magnesium ribbon. This can be done by gently scraping the ribbon with a knife or using fine sandpaper to remove any dirt or oxide layers.

2. Chemical cleaning:
Chemical cleaning involves using a suitable cleaning agent to dissolve or remove impurities from the surface of the ribbon. One common method is to immerse the ribbon in dilute hydrochloric acid (HCl) or sulfuric acid (H2SO4) to dissolve any oxide layers and remove impurities. After cleaning, the ribbon should be rinsed with distilled water to remove any remaining traces of the cleaning agent.

Conclusion:
Cleaning the magnesium ribbon before burning it in air is essential to ensure a more accurate and efficient combustion process. By removing impurities and oxide layers from the ribbon, the combustion reaction can proceed smoothly, resulting in a brighter and more visible flame. Proper cleaning methods, such as mechanical or chemical cleaning, should be employed to prepare the ribbon for combustion.