1. 2Mg + O₂ → 2MgO How many moles of MgO form if 6mol of oxygen react? *
2. 2Mg + O₂ → 2MgO How many moles of oxygen are required to react with 3.6mol of magnesium?
3. 2Mg + O₂ → 2MgO How many moles of magnesium are required to produce 5.5mol of MgO?

12 moles of MgO

1.8 moles of O₂

5.5 moles of Mg

Explanation:

These questions are all related and they involve comparing the number of moles of reactant to products.

Here we use molar relationship because they express what happens in a reaction much more better.

Problem 1:

                     2Mg    +     O₂     →    2MgO

We work from the known to the unknown;

              The known is oxygen gas;  which is 6moles

                       Unknown is MgO;

                    1 mole of O₂ produced 2 mole of MgO

                    6 moles of O₂ will produce  (6 x 2) moles of MgO

                                                                    = 12 moles of MgO

Problem 2:

               2Mg    +     O₂     →    2MgO

            Known;  3.6 moles of Magnesium

            Unknown;  number of moles of oxygen;

            2 moles of Mg reacted with 1 mole of O₂

          3.6 moles of Mg will react with     = 1.8 moles of O₂

Problem 3:

             2Mg    +     O₂     →    2MgO

           Known: number of of moles of MgO  = 5.5moles

           Unknown: number of moles of Mg = ?

          2 moles of MgO will be produced from 2 moles of Mg

         5.5 moles of MgO will be produced from   = 5.5 moles of Mg

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.