Answer:
H2 is the limiting reactant.
Step-by-step explanation:
From the diagram above:
H2 => White ball
O2 => Red ball
Before the reaction
H2 => White ball => 10
O2 => Red ball => 7
After the reaction
H2O => White and red ball => 10
O2 => 2
From the simple illustration above, we can see that all the H2 were used up in the reaction but there are left over of O2.
This simply means that H2 is the limiting reactant as all of it is used up in the reaction while O2 is the excess reactant as there are leftover.