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

Assertion (A) : Magnesium ribbon is cleaned with water before burning . Reason (R ) : MgO layer is formed on magnesium ribbon , on exposure to atmosphere .

A burning magnesium ribbon will continue to burn in

(a) Define the following in terms of gain or loss of hydrogen with one example each: (i) oxidatin (ii) reduction (b) When a magnesium ribbon is heated, it burns in air to form magnesium oxide. Write a balanced chemical equation for this reactin. Name (i) substance oxidised, and (ii) substance reduced.

Why does magnesium ribbon start floating in hot water?

Magnesium ribbon on burning in air produces