C2H2 + 3O2 ---------> 2H2O + 2CO2

Question

What is the volume of Oxygen required for the complete combination of 12.5cm^3 of ethene.

Answer 1

You don't have a balanced equation. Here is a correct one.
2C2H2 + 5O2 ---------> 2H2O + 4CO2
Here is a short cut you can use when gases are involved; i.e., use volumes as if they were mols.
12.5 cc C2H2 x (5 mols O2/4 mols C2H2) = ? cc O2 required.