Question

what is meant by 250ml of 0.1M oxalic acid solution

Answer 1

oxalic acid is $C_{2} H_{2 } O_{4}$
Now, 0.1 defines its concentration or molarity in 250ml solution.
Also, conc. or M(molarity)=n(moles)/volume.
=> in this case, 0.1=n/0.25           (as volume in liters)