Question

describe how to prepare about 125 mL of 25 % (m/v) of sodium oxalate (Na2C2O4) solution

Answer 1

Find mass of $Na_2C_2O_4$

$m= 0.125 L \times 0.25 = 0.0313 g$

So we should carefully measure 0.0313 g of $Na_2C_2O_4$ , put it in 500 ml beaker and add necessary volume of water until it reaches the line 125 ml. Also you may use conical flask of 125 ml volume instead of beaker.