Give the correct balanced equation for the single replacement reaction of magnesium with aluminum oxide. a) mg + alo → mgo + al b) mg + al2o3 → mgo + al c) 3mg + al2o3 → 3mgo + 2al d) mg + al2o3 → mgo3 + al2

Answer is "C".

Explanation

Single replacement reaction is a type of reaction which one reactant reacts with another and makes a product by replacing one element by another. 

Mg (Magnesium) reacts with Al₂O₃ (Aluminium oxide) and produces MgO (Magnesium oxide) and Al (Aluminium) as products. Here Al is replaced by Mg. Reaction is 
             Mg + Al₂O₃ → MgO + Al

To balance the reaction equation, both left and right hand sides should have same number of atoms in each element.
Here, 
 Left Hand Side has                                             Right Hand Side has
   Mg = 1 atom                                                         Mg = 1 atom
   Al = 2 atom                                                           Al = 1 atom
   O = 3 atom                                                           O = 1 atom

First step : balance the O atoms in both sides. To do that "3" should be added before MgO. 

Second step : After balancing O atoms, there will be 3 Mg atoms in right hand side. Hence to balance Mg atoms again "3" should be added before Mg in left hand side

Third step : as the final step balance the Al atoms by adding "2" before Al in the right hand side.

Then final balanced equation should be 
              3Mg + Al₂O₃ → 3MgO + 2Al

 

They are all full and don't need any more electrons in there outer shell.