In this reaction, two elements (Mg and ) combine to form a single compound, MgO. Hence, this reaction is an example of chemical combination or synthesis. Here as the element Mg is oxidized in the presence of to form MgO. This is referred to as combustion reaction. In combustion reaction, elements or compounds react with oxygen to give their respective oxides.
So we know the number of moles of each compound. If we need to know the concentration we must know the number of moles that the compounds react with...