Question

What happens when magnesium ribbon is ignited? Give chemical reaction

Answer 1

Magnesium burns in air to give magnesium oxide giving white light and releasing enormous energy.
2Mg + O₂ ---> 2MgO

Answer 2

When a magnesium ribbon is heated, it burns in air with a dazzling white flame to form a white powder called magnesium oxide. Actually, on heating, magnesium combines with oxygen present in air to form magnesium oxide...
 Magnesium    +    Oxygen                           Magnesium oxide                           
(As ribbon)          (From air)         ⇒               (white powder)
                                 OR
 Mg  +  $O_{2}$    ⇒   MgO