The Oxalic acid
An equivalent is the quantity of acid that can react with a substance in a specific reaction that is not indicated in the question.
The oxalic acid can react as acid with a basic and its equivalent mass is the half of its MM having two acid atoms of Hydrogen.
It can also react with an oxidant, buying two electrons and increasing the oxidation number of its Carbon from 3 to 4. Fortunately also this time its equivalent mass is the half of its MM.
So your solution contains M= 0,01 equivalents x 45,0 g/eq = 0,45 g