Answer
See the answer below.
Work Step by Step
First ionization:
$H_2C_2O_4+H_2O\leftrightarrow H_3O^++HC_2O_4^-$
Second ionization:
$HC_2O_4^-+H_2O\leftrightarrow H_3O^++C_2O_4^{2-}$
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