(43) How many moles of the excess reagent remain unreacted? [1] 1 mol [2] 2 mol [3] 4 mol [4] 5 mol?

Update: The balanced reaction:   
  
2Mg + O2 → 2MgO   
  
In the above reaction, 2 moles of Mg and 5 moles of O2 are allowed to react. 
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