By using the following formula we can calculate the volume;
C₁V₁ = C₂V₂
C₁ = concentration of starting solution = 1.0m
V₁ = volume of starting solution that is needed to make the dilution = ?
C₂ = Desired concentration of final solution = 0.1m
V₂ = desired volume of final solution = 250ml
Now putting the values in the formula;
1 x V₁ = 0.1 x 250
V₁ = 25ml
Thus, the answer is 25ml.