2.0 molar solution is obtained , when 0.5 mole solute is dissolved in

We know that  

$\text{ Molarity }=\frac{\text{ Number of moles of solute }}{\text{ Volume of solution in litre }}$

$\begin{array}{r}\therefore 2.0=\frac{0.5}{\text{ Volume of solution in litre }}\\ \therefore \text{ Volume of solution in litre }\\ =\frac{0.5}{2.0}=0.250\text{ litre }=250\mathrm{ml}.\end{array}$