Step 1
The reaction is written and balanced as:
C2H4(g) + 302(g) → 2CO2(g) + 2H2O(g)
Step 2
Oxidation states are analyzed
For O2)
On the left, its oxidation state is 0 (O2)
On the right, it is -2 (H2O)
Step 3
The half-reaction is written as:
6 O + 12 e- => 6 O2-
Therefore, O2 is being reduced
Answer: O2
