Answer :
Magnesium ribbon is rubbed before burning to remove the layer of basic magnesium carbonate that inhibits its reactivity. This ensures a vigorous reaction with oxygen to form magnesium oxide, which is important for chemistry demonstrations and experiments. Option b is correct.
Magnesium ribbon is rubbed before burning to remove a coating. This coating is composed of basic magnesium carbonate which forms on the ribbon's surface upon exposure to air. This is because magnesium metal reacts with carbon dioxide in the atmosphere to form magnesium oxycarbonate, a form of basic magnesium carbonate, which acts as a protective layer and decreases the metal's reactivity through passivation.
Before igniting the magnesium ribbon in experiments, we rub off this layer to ensure that the metal can react readily with oxygen when heated, allowing it to burn with a bright white flame. Upon burning, magnesium reacts with oxygen to form magnesium oxide, observed as a fine white powder.
The cleaning process of the magnesium ribbon is necessary for accurate experiments and demonstrations in chemistry, providing insight into the metal's properties, reactivity, and the resulting compounds from combustion. Option b is correct.
