The formula for the oxalate ion is #C_2O_4^(2-)#. What would you predict the formula for oxalic acid to be?
Add two protons.............?
An acid consists of positively-charged hydrogen ion(s) and an anion. This can be symbolized in a chemical equation:
"The Hill system (or Hill notation) is a system of writing empirical chemical formulas, molecular chemical formulas and components of a condensed formula such that the number of carbon atoms in a molecule is indicated first, the number of hydrogen atoms next, and then the number of all other chemical elements subsequently, in alphabetical order of the chemical symbols. When the formula contains no carbon, all the elements, including hydrogen, are listed alphabetically."
Therefore the formula should be