Answer: 1.00 L
Explanation: Pressure and Volume are inversely proportionate. The volume increases at a factor of 2, from 1.00 L to 2.00 L. This means the pressure would decrease by a factor of 2, from 4.00 atm to 2.00 atm. Think about it, if you had a box and it doubled in the space, the same amount of gas is still in the container and the pressure would be half as much as these gas particles would have half the amount of collisions against the walls