Well, oxalato ion is OXIDIZED to give carbon dioxide gas.....
Mass and charge are balanced so this is a valid oxidation reaction. And for every oxidation there is a corresponding reduction.
Ferric ion is reduced to ferrous ion, and oxalate ion is oxidized to carbon dioxide.
Do you follow?
Here's what I get.
You can find the general technique for balancing redox equations in acid solution here.
Step 1: Write the two half-reactions
Step 2: Balance all atoms other than
Step 3: Balance
Step 4: Balance
Step 5: Balance charge
We see that
Step 6: Equalize electrons transferred
Step 7: Add the two half-reactions
Step 8: Check mass balance
Step 9: Check charge balance
The balanced equation is