Could you please explain the question in the picture I have linked thank you!

Question X In order to make the precipitate of calcium oxalate as complete as possible, (refer to lab manual) one should one use (circle one answer) (a) the soluble salt (NH4)2C2O4 (b) the weak acid H2C2O4 Question Y To yield the highest concentration of C2O42 ions, which of the (refer to lab manual) following should be added to the weak acid H2C2O4 ? (circle one answer) (a) a strong base (b) a strong acid Question Z The acidity of a solution is more important in the precipitation of (refer to lab manual) (circle one answer) (a) the salt of a strong acid (b) the salt of a weak acid