We have to calculate volume of gas at 700 mm Hg pressure.
The answer is 457.14 ml.
The pressure can be calculated by using Boyle's law. At constant temperature, for a given mass of an ideal gas pressure is inversely related to volume.
As per Boyle's law, P₁V₁ = P₂V₂, where P is pressure and V is volume of gas.
Given, P₁= 800 mm Hg, V₁= 400 ml and P₂= 700 mm Hg, V₂=?
800 X 400 = 700 X V₂
So, V₂= (800X400)/700 = 457.14 ml