Question

Users Please answer to the question no. 23.

Answer 1

    MgO is the ash collected,.

as, when Mg is burnt in Oxygen,

The following reaction takes place,.

$2Mg +O_2 --\ \textgreater \ 2MgO$



Magnesium is cleaned with paper because,
we need to remove the layer of magnesium carbonate (which is formed when Magnesium is exposed to air,it reacts with $CO_2$ to form that layer.  )        
to observe white dazzling flame,..
 Hope it Helps

Answer 2

because magnesium ribbon kept in air so it forms magnesium carbonate due to its reaction with carbondioxide so it need to be rubbed with paper to remove the coat, white ash is magnesium oxide because while burning magnesium reacts with oxygen