To solve this problem we apply the Charles's law which states that "the volume of a fixed mass of a gas varies directly as its absolute temperature if the pressure is constant".
Number of moles in 250ml of 2.5M KCl is (250÷1000)litres×2.5M so we divide these moles by 8M. The answer gotten will be in litres so multiply by 1000 to get it in ml