The formula is given by Molarity of mgso4 required for the titration * Volume of mgso4 for the titration = Molarity of mgso4 used to make the solution * Volume of mgso4 used to make the solution.
So we have 0.5 * Volume of mgso4 = 100 * 0.2
So Volume of mgso4 = (100 * 0.2)/ 0.5
Volume = 20/0.5 = 40ml = 40 * 10^(-3)
