Question

why should magnesium ribbon be cleaned before burning in air give reason

Answer 1

$hey \: dear \: here \: is \: your \: answer$

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☢ the magnesium ribbon rubbed by sand paper before burning because it contains some impurity such as magnesium carbonate on its surface so it is necessary to remove this layer so that the magnesium ribbon can burn smoothly otherwise it will burn spontaneously.

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$hope \: this \: helps \: u \: dear$
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Answer 2

magnesium ribbon should be cleaned so as to remove the layer of magnesium oxide that is formed as a result of the reaction of magnesium with oxygen in air.