Magnesium + oxygen ------------> Magnesium oxide
2Mg + O2 -----------------------> 2MgO
We have been given that Mg reacts with Oxygen in the fixed ratio of 3 : 2by mass.
3g of Mg requires = 2g of oxygen
So, 24g of Mg requires =
= 16g
So, 24g of Mg requires, 16g of oxygen to combine.